Bug 1784737 - Compile standalone compiler-rt in C++17 mode. r=andi

Differential Revision: https://phabricator.services.mozilla.com/D154771

build/build-clang/clang-trunk.json

@@ -7,6 +7,7 @@
         "bug47258-extract-symbols-mbcs.patch",
         "fuzzing_ccov_build_clang_12.patch",
         "win64-no-symlink_clang_16.patch",
+        "compiler-rt-c++17.patch",
         "revert-llvmorg-15-init-13446-g7524fe962e47.patch",
         "revert-llvmorg-14-init-14141-gd6d3000a2f6d.patch",
         "revert-llvmorg-14-init-11890-gf86deb18cab6.patch"

build/build-clang/compiler-rt-c++17.patch

@@ -0,0 +1,14 @@
+diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
+index 4f8e095c3b91..057dbf645450 100644
+--- a/compiler-rt/CMakeLists.txt
++++ b/compiler-rt/CMakeLists.txt
+@@ -69,6 +69,9 @@ set(COMPILER_RT_BAREMETAL_BUILD OFF CACHE BOOL
+ 
+ if (COMPILER_RT_STANDALONE_BUILD)
+   load_llvm_config()
++  set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
++  set(CMAKE_CXX_STANDARD_REQUIRED YES)
++  set(CMAKE_CXX_EXTENSIONS NO)
+   if (TARGET intrinsics_gen)
+     # Loading the llvm config causes this target to be imported so place it
+     # under the appropriate folder in an IDE.