Fix GNU-style flag passing to MSVC frontend

[annihilatorq]

Issue

When building glaze with clang-cl, the build fails because some branches in tests/CMakeLists.txt and fuzzing/CMakeLists.txt select GNU-style flags based only on CMAKE_<LANG>_COMPILER_ID=Clang

This is incorrect for clang-cl: although the compiler ID is Clang, its frontend is MSVC-compatible and therefore expects MSVC-style command-line options. To solve this issue, CMake introduced CMAKE_LANG_COMPILER_FRONTEND_VARIANT flag in v3.14

Fix

This PR updates the compiler checks in tests/CMakeLists.txt and fuzzing/CMakeLists.txt to account for the frontend variant, so clang-cl no longer enters the GNU-style flag branch. As a result, the affected targets configure and build correctly with clang-cl

gotta see what CI will say, and if there are any issues (which shouldn't be the case, but who knows 😁), I'll take care of them

P.S. I also removed target_link_options(glz_test_common INTERFACE -ftime-trace) since target_link_options() applies to the linker, while afaik the flag is intended for compile-time tracing

[annihilatorq]

I also wanted to ask if there's a reason why glaze hasn't added a basic workflow for building and testing with clang-cl?
If it's because of a lack of time or because this task isn't a high priority, I'd be more than happy to help

[annihilatorq]

hmm, I guess we can also simplify these checks, so instead of

if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" OR CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "MSVC")
  # Something for compiler with MSVC command line style
endif()

we can use

if(MSVC)
  # Something for compiler with MSVC command line style
endif()

since, as stated in CMake MSVC variable documentation, it is Set to true when the compiler is some version of Microsoft Visual C++ or another compiler simulating the Visual C++ cl command-line syntax.

should we change our current approach (CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "MSVC" to MSVC), or would glaze prefer to stick to a single style for all compilers?

[annihilatorq]

seems like glaze already uses if(MSVC)

glaze/CMakeLists.txt

Line 22 in 6a7d699

if (MSVC)

so I replaced the long if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" OR CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "MSVC") with if(MSVC)

[stephenberry]

Thanks for this contribution for clang-cl. I'll look it over in a bit more detail ASAP. But, I'm also open for a PR that tests clang-cl if you'd like to add it.

[stephenberry]

Looks good!