[clang] [FreeBSD] Support -stdlib=libstdc++ (PR #126302)

[Alexander Richardson via cfe-commits]

arichardson wrote:

> It's not missing as in like someone forgot. It is intentional. Same goes for FreeBSD and OpenBSD's Drivers. The base OS uses libc++ and anything else is not supported.

You can install it from ports though and it should be possible to use that?

https://github.com/llvm/llvm-project/pull/126302