[OpenMP] Fix clang-cl build error regarding TSX intrinsics

Fix for https://bugs.llvm.org/show_bug.cgi?id=49339 The CMake check for the RTM intrinsics needs the -mrtm flag to be set during the test. This way clang-cl correctly detects it has the _xbegin() intrinsic. Otherwise, the CMake check fails. Differential Revision: https://reviews.llvm.org/D97413

Author: Peyton, Jonathan L

openmp/runtime/cmake/config-ix.cmake

@@ -175,6 +175,10 @@ if (IA32 OR INTEL64)
  }
  int main() { int a = __kmp_umwait(0, 1000); return a; }")
  check_cxx_source_compiles("${source_code}" LIBOMP_HAVE_WAITPKG_INTRINSICS)
+ set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+ if (LIBOMP_HAVE_MRTM_FLAG)
+ set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -mrtm")
+ endif()
  set(source_code "// check for attribute rtm and rtm intrinsics
  #ifdef IMMINTRIN_H
  #include <immintrin.h>
@@ -191,6 +195,7 @@ if (IA32 OR INTEL64)
  int main() { int a = __kmp_xbegin(); return a; }")
  check_cxx_source_compiles("${source_code}" LIBOMP_HAVE_RTM_INTRINSICS)
  set(CMAKE_REQUIRED_DEFINITIONS)
+ set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
 endif()
 
 # Find perl executable