[libcxx-commits] [libcxx] [libc++] Avoid calling `setlocale` in `do_unshift` when unnecessary (PR #117153)

[Martin Storsjö via libcxx-commits]

mstorsjo wrote:

Hopefully @tahonermann has time to look at this; I'm unfortunately not very familiar with this area. In particular, I don't quite follow how the PR description (which sounds very reasonable) maps to this piece of code - how `mbsinit(mbstate_t*)` checks whether there are buffered characters or not. (And wouldn't we want to do that check only in some destructor, rather than adding a check every time we do `do_unshift`?)

https://github.com/llvm/llvm-project/pull/117153