[libcxx-commits] [libcxx] [libc++] Only include <setjmp.h> from the C library if it exists (PR #81887)

[Louis Dionne via libcxx-commits]

ldionne wrote:

This broke some code downstream and we think this could have a negative impact on freestanding users (who are most likely not to have a `setjmp.h` header around), so I'm planning to backport this to LLVM 18.

https://github.com/llvm/llvm-project/pull/81887