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

[via cfe-commits]

dankm wrote:

> If I understand correctly this means in effect `-stdlib=` becomes a don't-care when linking C, and anyhow it already had no effect.

That's correct. It was previously a harmless warning at link time, and is now (with this change) completely ignored.

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