[libcxx-commits] [libcxx] [libc++] Fix `regex_search` to match `$` alone with `match_default` flag (PR #77256)

[Louis Dionne via libcxx-commits]

ldionne wrote:

This seems broken to me -- the pattern `^b*$` shouldn't match `a`. @SanjayMarreddi if you're unsure how to fix this forward, let's revert the commit and add this regression test case, and then work on re-landing the patch without breaking that case. Let me know if you need help with the revert.

https://github.com/llvm/llvm-project/pull/77256