[libcxx-commits] [libcxx] [llvm] [libc++] Refactor the configuration macros to being always defined (PR #112094)

[Martin Storsjö via libcxx-commits]

mstorsjo wrote:

> As you mentioned, checking libc++ internal macros is not something we support. If we supported that, we couldn't make any modifications to the code base without breaking people.

Yep - I guess this is a case of us thinking "how bad can it be" (https://xkcd.com/292/).

I guess I assumed that if things change/break (e.g. if the macro is renamed) we'd fail by not picking up libcxx built with pthreads (which, TBH, is a very rare configuration - I think this was added to work with libstdc++ builds on top of pthread, which is a very common configuration). I.e. we assumed that if things break, we'd get false negatives, but instead we get false positives for the condition here.

https://github.com/llvm/llvm-project/pull/112094