Bug 1751824 - Fixup for macos compiler-rt build. CLOSED TREE

Applying all the patches from build-clang enabled the patch for macos
cross compiles that adds a -target argument based on
LLVM_DEFAULT_TARGET_TRIPLE, that we weren't setting.

Differential Revision: https://phabricator.services.mozilla.com/D137252

taskcluster/scripts/misc/build-compiler-rt.sh

@@ -62,6 +62,7 @@ case "$target" in
     -DDARWIN_osx_SYSROOT=$MOZ_FETCHES_DIR/MacOSX11.0.sdk
     -DDARWIN_macosx_OVERRIDE_SDK_VERSION=11.0
     -DDARWIN_osx_BUILTIN_ARCHS=$arch
+    -DLLVM_DEFAULT_TARGET_TRIPLE=$target
   "
   # compiler-rt build script expects to find `codesign` in $PATH.
   # Give it a fake one.