[libcxx-commits] [libcxx] [libc++] Add #if 0 block to all the top-level headers (PR #119234)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

LGTM assuming:
1. Green CI
2. When you substitute back `#if 0\n#else` and `#endif // 0` to nothing and run clang-format, this patch is a no-op.

This should be easy to check.

https://github.com/llvm/llvm-project/pull/119234