diff --git a/build/build-clang/build-clang.py b/build/build-clang/build-clang.py
index a2271d0f9e28..dd1a18ef9232 100755
--- a/build/build-clang/build-clang.py
+++ b/build/build-clang/build-clang.py
@@ -242,7 +242,6 @@ def build_one_stage(
         # libc++ doesn't build with MSVC because of the use of #include_next.
         if is_final_stage and os.path.basename(cc[0]).lower() != "cl.exe":
             cmake_args += [
-                "-DLLVM_FORCE_BUILD_RUNTIME=ON",
                 "-DLLVM_TOOL_LIBCXX_BUILD=%s" % ("ON" if build_libcxx else "OFF"),
                 # libc++abi has conflicting definitions between the shared and static
                 # library on Windows because of the import library for the dll having
@@ -252,13 +251,9 @@ def build_one_stage(
             ]
         if not is_final_stage:
             cmake_args += [
-                "-DLLVM_ENABLE_PROJECTS=clang;compiler-rt",
+                "-DLLVM_ENABLE_PROJECTS=clang",
                 "-DLLVM_INCLUDE_TESTS=OFF",
                 "-DLLVM_TOOL_LLI_BUILD=OFF",
-                "-DCOMPILER_RT_BUILD_SANITIZERS=OFF",
-                "-DCOMPILER_RT_BUILD_XRAY=OFF",
-                "-DCOMPILER_RT_BUILD_MEMPROF=OFF",
-                "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF",
             ]
 
         # There is no libxml2 on Windows except if we build one ourselves.
@@ -512,7 +507,6 @@ def main():
     extra_source_dir = source_dir + "/clang-tools-extra"
     clang_source_dir = source_dir + "/clang"
     lld_source_dir = source_dir + "/lld"
-    compiler_rt_source_dir = source_dir + "/compiler-rt"
     libcxx_source_dir = source_dir + "/libcxx"
     libcxxabi_source_dir = source_dir + "/libcxxabi"
 
@@ -647,13 +641,10 @@ def main():
         for p in config.get("patches", []):
             patch(p, source_dir)
 
-    compiler_rt_source_link = llvm_source_dir + "/projects/compiler-rt"
-
     symlinks = [
         (clang_source_dir, llvm_source_dir + "/tools/clang"),
         (extra_source_dir, llvm_source_dir + "/tools/clang/tools/extra"),
         (lld_source_dir, llvm_source_dir + "/tools/lld"),
-        (compiler_rt_source_dir, compiler_rt_source_link),
         (libcxx_source_dir, llvm_source_dir + "/projects/libcxx"),
         (libcxxabi_source_dir, llvm_source_dir + "/projects/libcxxabi"),
         (source_dir + "/cmake", llvm_source_dir + "/projects/cmake"),
diff --git a/taskcluster/ci/toolchain/clang.yml b/taskcluster/ci/toolchain/clang.yml
index b4ebbb58d497..b20f2c1460ca 100644
--- a/taskcluster/ci/toolchain/clang.yml
+++ b/taskcluster/ci/toolchain/clang.yml
@@ -149,6 +149,7 @@ linux64-clang-13-profile:
             - clang-13
         toolchain:
             - linux64-clang-13-stage1
+            - linux64-x64-compiler-rt-13
             - linux64-toolchain-sysroot
 
 linux64-clang-13:
@@ -189,7 +190,7 @@ linux64-clang-13-android-cross:
         symbol: TL(clang13-android)
     run:
         using: toolchain-script
-        script: repack-clang-linux-cross.sh
+        script: repack-clang.sh
         toolchain-alias: linux64-clang-android-cross
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
@@ -208,7 +209,7 @@ linux64-clang-13-aarch64-cross:
     worker:
         max-run-time: 600
     run:
-        script: repack-clang-linux-cross.sh
+        script: repack-clang.sh
         toolchain-alias: linux64-clang-aarch64-cross
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
@@ -224,7 +225,7 @@ linux64-clang-13-macosx-cross:
     worker:
         max-run-time: 600
     run:
-        script: repack-clang-linux-macosx-cross.sh
+        script: repack-clang.sh
         toolchain-alias: linux64-clang-macosx-cross
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
@@ -242,7 +243,7 @@ linux64-clang-13-win-cross:
     worker:
         max-run-time: 600
     run:
-        script: repack-clang-linux-win-cross.sh
+        script: repack-clang.sh
         toolchain-alias: linux64-clang-win-cross
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
@@ -276,9 +277,10 @@ macosx64-clang-13-raw:
             - clang-13
         toolchain:
             - linux64-cctools-port
-            - linux64-clang-13-macosx-cross
+            - linux64-clang-13-stage1
             - linux64-clang-13-profile
             - macosx64-sdk-11.0
+            - macosx64-x64-compiler-rt-13
             - wasm32-wasi-compiler-rt-13
 
 macosx64-clang-13:
@@ -293,7 +295,7 @@ macosx64-clang-13:
     run-on-projects:
         - trunk
     run:
-        script: repack-clang-linux-macosx-cross.sh
+        script: repack-clang.sh
         toolchain-alias:
             - macosx64-clang
             - macosx64-clang-toolchain
@@ -332,9 +334,10 @@ macosx64-aarch64-clang-13-raw:
             - clang-13
         toolchain:
             - linux64-cctools-port
-            - linux64-clang-13-macosx-cross
+            - linux64-clang-13-stage1
             - linux64-clang-13-profile
             - macosx64-sdk-11.0
+            - macosx64-aarch64-compiler-rt-13
             - wasm32-wasi-compiler-rt-13
 
 macosx64-aarch64-clang-13:
@@ -349,7 +352,7 @@ macosx64-aarch64-clang-13:
     run-on-projects:
         - trunk
     run:
-        script: repack-clang-linux-macosx-cross.sh
+        script: repack-clang.sh
         toolchain-alias: macosx64-aarch64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
@@ -391,6 +394,7 @@ win64-clang-13-raw:
         toolchain:
             - win64-clang-13-stage1
             - wasm32-wasi-compiler-rt-13
+            - win64-compiler-rt-13
 
 win64-clang-13:
     description: "Clang-cl 13 toolchain build"
@@ -404,7 +408,7 @@ win64-clang-13:
     run-on-projects:
         - trunk
     run:
-        script: repack-clang-linux-win-cross.sh
+        script: repack-clang.sh
         toolchain-alias: win64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
diff --git a/taskcluster/scripts/misc/build-clang.sh b/taskcluster/scripts/misc/build-clang.sh
index 2c25196d9645..d8e5ee6aa174 100755
--- a/taskcluster/scripts/misc/build-clang.sh
+++ b/taskcluster/scripts/misc/build-clang.sh
@@ -16,6 +16,9 @@ if [ -d "$MOZ_FETCHES_DIR/binutils/bin" ]; then
   export PATH="$MOZ_FETCHES_DIR/binutils/bin:$PATH"
 fi
 
+# Make the installed compiler-rt(s) available to clang.
+UPLOAD_DIR= taskcluster/scripts/misc/repack-clang.sh
+
 case "$CONFIGS" in
 *macosx64*)
   # these variables are used in build-clang.py
diff --git a/taskcluster/scripts/misc/repack-clang-linux-cross.sh b/taskcluster/scripts/misc/repack-clang-linux-cross.sh
deleted file mode 100755
index 74b98b201262..000000000000
--- a/taskcluster/scripts/misc/repack-clang-linux-cross.sh
+++ /dev/null
@@ -1,18 +0,0 @@
-#!/bin/bash
-set -x -e -v
-
-# This script is for building clang for cross Linux targets on a Linux host.
-
-cd $MOZ_FETCHES_DIR
-
-# We have a native linux64 toolchain in $MOZ_FETCHES_DIR/clang
-# We have some linux compiler-rts in $MOZ_FETCHES_DIR/compiler-rt*
-clang_lib=$(echo $PWD/clang/lib/clang/*/lib)
-find compiler-rt-*/lib/linux -type f | while read f; do
-  cp -n $f $clang_lib/linux
-done
-
-tar -caf clang.tar.zst clang
-
-mkdir -p $UPLOAD_DIR
-mv clang.tar.zst $UPLOAD_DIR
diff --git a/taskcluster/scripts/misc/repack-clang-linux-macosx-cross.sh b/taskcluster/scripts/misc/repack-clang-linux-macosx-cross.sh
deleted file mode 100755
index 345271f13029..000000000000
--- a/taskcluster/scripts/misc/repack-clang-linux-macosx-cross.sh
+++ /dev/null
@@ -1,30 +0,0 @@
-#!/bin/bash
-set -x -e -v
-
-# This script is for building clang for macOS targets on a Linux host,
-# including native macOS Compiler-RT libraries.
-
-cd $MOZ_FETCHES_DIR
-
-# We have a native linux64 toolchain in $MOZ_FETCHES_DIR/clang
-# We have a native aarch64 macos compiler-rt in $MOZ_FETCHES_DIR/compiler-rt-aarch64-apple-darwin
-# We have a native x86_64 macos compiler-rt in $MOZ_FETCHES_DIR/compiler-rt-x86_64-apple-darwin
-clang_lib=$(echo clang/lib/clang/*/lib)
-mkdir -p $clang_lib/darwin
-find compiler-rt-*/lib/darwin -type f -printf '%f\n' | sort -u | while read f; do
-  f=lib/darwin/$f
-  if [ -f compiler-rt-aarch64-apple-darwin/$f -a -f compiler-rt-x86_64-apple-darwin/$f ]; then
-    # For compiler-rt files that exist on both ends, merge them
-    $MOZ_FETCHES_DIR/cctools/bin/lipo -create compiler-rt-{aarch64,x86_64}-apple-darwin/$f -output $clang_lib/darwin/${f##*/}
-  elif [ -f compiler-rt-aarch64-apple-darwin/$f ]; then
-    # For compiler-rt files that exist on either end, copy the existing one
-    cp compiler-rt-aarch64-apple-darwin/$f $clang_lib/darwin
-  else
-    cp compiler-rt-x86_64-apple-darwin/$f $clang_lib/darwin
-  fi
-done
-
-tar caf clang.tar.zst clang
-
-mkdir -p $UPLOAD_DIR
-mv clang.tar.zst $UPLOAD_DIR
diff --git a/taskcluster/scripts/misc/repack-clang-linux-win-cross.sh b/taskcluster/scripts/misc/repack-clang-linux-win-cross.sh
deleted file mode 100755
index f471363bd2f7..000000000000
--- a/taskcluster/scripts/misc/repack-clang-linux-win-cross.sh
+++ /dev/null
@@ -1,21 +0,0 @@
-#!/bin/bash
-set -x -e -v
-
-# This script is for building clang for windows targets on a Linux host,
-# including native Windows Compiler-RT libraries.
-
-cd $MOZ_FETCHES_DIR
-
-# We have a native linux64 toolchain in $MOZ_FETCHES_DIR/clang
-# We have a native x86 windows compiler-rt in $MOZ_FETCHES_DIR/compiler-rt-i686-pc-windows-msvc
-# We have a native x86_64 windows compiler-rt in $MOZ_FETCHES_DIR/compiler-rt-x86_64-pc-windows-msvc
-clang_lib=$(echo clang/lib/clang/*/lib)
-mkdir -p $clang_lib/windows
-cp compiler-rt-i686-pc-windows-msvc/lib/windows/* $clang_lib/windows
-cp compiler-rt-x86_64-pc-windows-msvc/lib/windows/* $clang_lib/windows
-
-tar caf clang.tar.zst clang
-
-# Put a tarball in the artifacts dir
-mkdir -p $UPLOAD_DIR
-cp clang.tar.zst $UPLOAD_DIR
diff --git a/taskcluster/scripts/misc/repack-clang.sh b/taskcluster/scripts/misc/repack-clang.sh
new file mode 100755
index 000000000000..6331aca5ad43
--- /dev/null
+++ b/taskcluster/scripts/misc/repack-clang.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+set -x -e -v
+
+shopt -s nullglob
+
+# This script is for repacking clang for cross targets on a Linux host.
+
+cd $MOZ_FETCHES_DIR
+
+# We have a clang toolchain in $MOZ_FETCHES_DIR/clang
+# We have some compiler-rts in $MOZ_FETCHES_DIR/compiler-rt*
+# We copy everything from the compiler-rts into clang/lib/clang/$version
+clang_dir=$(echo clang/lib/clang/*/include)
+clang_dir=${clang_dir%/include}
+[ -n "$clang_dir" ] && for c in compiler-rt*; do
+  find $c -mindepth 1 -type d | while read d; do
+    mkdir -p "$clang_dir/${d#compiler-rt-*/}"
+    find $d -mindepth 1 -maxdepth 1 -not -type d | while read f; do
+      target_file="$clang_dir/${f#compiler-rt-*/}"
+      case $d in
+      compiler-rt-*/lib/darwin)
+        if [ -f "$target_file" ]; then
+          # Unify overlapping files for darwin/
+          $MOZ_FETCHES_DIR/cctools/bin/lipo -create "$f" "$target_file" -output "$target_file.new"
+          mv "$target_file.new" "$target_file"
+          continue
+        fi
+        ;;
+      esac
+      if [ -f "$target_file" ] && ! diff -q "$f" "$target_file" 2>/dev/null; then
+        echo "Cannot copy $f because it is already in ${target_file%/*}" >&2 && exit 1
+      fi
+      cp "$f" "$target_file"
+    done
+  done
+done
+
+if [ -n "$UPLOAD_DIR" ]; then
+  tar caf clang.tar.zst clang
+  mkdir -p $UPLOAD_DIR
+  mv clang.tar.zst $UPLOAD_DIR
+fi