[BUG] cmake generate fails with msvc and clang-cl

[hsdk123]

Describe the bug A clear and concise description of what the bug is.

cmake fails at https://github.com/google/benchmark/blob/main/CMakeLists.txt#L298

when using cmake on msvc with clang-cl settings https://learn.microsoft.com/en-us/cpp/build/clang-support-cmake?view=msvc-170

System Which OS, compiler, and compiler version are you using:

• OS: Windows
• Compiler and version:

  1> [CMake] CMAKE_C_COMPILER= C:/PROGRAM FILES/MICROSOFT VISUAL STUDIO/2022/COMMUNITY/VC/Tools/Llvm/x64/bin/clang-cl.exe
  1> [CMake] CMAKE_CXX_COMPILER= C:/PROGRAM FILES/MICROSOFT VISUAL STUDIO/2022/COMMUNITY/VC/Tools/Llvm/x64/bin/clang-cl.exe

To reproduce Steps to reproduce the behavior:

1. sync to commit ...
2. cmake/bazel...
3. make ...
4. See error

Expected behavior A clear and concise description of what you expected to happen.

Screenshots If applicable, add screenshots to help explain your problem.

Additional context Add any other context about the problem here.

[dmah42]

can you please set -DCXXFEATURECHECK_DEBUG=on, retry, and attach the cmake logs please? that should help us determine why the msvc+clang config is failing to identify a working regex solution.

(btw is it correct that both the C and C++ compiler are clang-cl? that's a little surprising to me as usually (not-windows) these are different binaries).