[llvm] [Support] Use std::filesystem::remove_all() in remove_directories() (PR #119146)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> > std::filesystem::remove_all(std::filesystem::__cxx11::path const&, std::error_code&)
> 
> It seems __cxx11 means c++11, not c++17.

I think that's unrelated - I would guess that it's some libstdc++ internal ABI grouping, where some classes had to break ABI betwen C++03 and C++11, and this belongs to the post-C++11 category.

https://github.com/llvm/llvm-project/pull/119146