[TSan] Add CMake check for minimal SDK requirements on Darwin

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

compiler-rt/lib/tsan/CMakeLists.txt

@@ -114,6 +114,14 @@ set(TSAN_RUNTIME_LIBRARIES)
 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})