[libcxx-commits] [libcxx] [libc++] Clean up windows macros (PR #207577)

[Nikolas Klauser via libcxx-commits]

philnik777 wrote:

@mstorsjo I've kept `_LIBCPP_MSVCRT` for now to keep the diff smaller and avoid the issue whether we should detect the libc at configure-time (IMO that's kinda orthogonal to the aim of this patch), but I'm happy with renaming it in a follow-up.

https://github.com/llvm/llvm-project/pull/207577