Fails with the following message in the error case:
```
CMake Error at /path/to/llvm-project/compiler-rt/lib/tsan/CMakeLists.txt:119 (message):
Building the TSan runtime requires at least macOS SDK 10.12
```
Fixes #44682.
https://bugs.llvm.org/show_bug.cgi?id=44682
Reviewed By: dmajor, delcypher
Differential Revision: https://reviews.llvm.org/D74501
add_compiler_rt_component(tsan)
if(APPLE)
+ # Ideally we would check the SDK version for the actual platform we are
+ # building for here. To make our lifes easier we assume the host SDK setup is
+ # sane and use the macOS SDK version as a proxy for aligned SDKs.
+ find_darwin_sdk_version(macosx_sdk_version "macosx")
+ if ("${macosx_sdk_version}" VERSION_LESS 10.12)
+ message(FATAL_ERROR "Building the TSan runtime requires at least macOS SDK 10.12 (or aligned SDK on other platforms)")
+ endif()
+
add_asm_sources(TSAN_ASM_SOURCES rtl/tsan_rtl_amd64.S rtl/tsan_rtl_aarch64.S)
set(TSAN_LINK_LIBS ${SANITIZER_COMMON_LINK_LIBS})