[compiler-rt] [libc++] Use -nostdlib++ on GCC unconditionally (PR #68832)

[via llvm-commits]

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

It's nice having CI for all the platforms, otherwise this would be harder to review and be confident about.

LGTM assuming everything passes.

https://github.com/llvm/llvm-project/pull/68832