[libcxx-commits] [libcxx] [llvm] [libcxx][llvm]: Fix misidentification of GNU-style clang as clang-cl (PR #225124)

[Martin Storsjö via libcxx-commits]

mstorsjo wrote:

Can you clarify the different cmake variables here - they're not immediately obvious as they're all named similar-ish.

`CMAKE_CXX_COMPILER_FRONTEND_VARIANT` - is this about whether using `clang-cl` command line syntax, as opposed to `clang` with the GNU style command line? Is there a reason for using this specifically here? The `MSVC` variable in cmake is also set for both actual MSVC `cl.exe` and with `clang-cl`.

`CMAKE_CXX_SIMULATE_ID` is set to `MSVC` for both `clang-cl`, and `clang` with an MSVC target, right?

Can you also briefly confirm that both `LIBCXX_TARGETING_CLANG_CL` and `CLANG_CL` only affect options specifically relating to the `cl.exe` style of command line options, not anything else?

It would be good to briefly rehash these details in the commit message (i.e. the PR description) to make it clear to both current and future readers.

https://github.com/llvm/llvm-project/pull/225124