[clang] [Driver] Silence stdlib warning when linking C on FreeBSD (PR #68011)

[via cfe-commits]

dankm wrote:

> Does this only affect cases where one passes `-stdlib=libc++`? What happens if somebody passes `-stdlib=libstdc++`?

It handles both cases. It simply claims all the `-stdlib=` arguments. This is the same behaviour as the Gnu driver used by Linux, but seems to diverge from Darwin.

https://github.com/llvm/llvm-project/pull/68011