prior to 18.0 to workaround libc++ having the wrong signature for
these functions.

Upstream issue: https://github.com/llvm/llvm-project/issues/64544

The preprocessor conditions were inverted for readability as the
conditions became more complex.

PiperOrigin-RevId: 557559472
Change-Id: Ibf7a2651e13a0d2a91846bc0d72ba3a44f56747b