[clang] [clang][driver] Don't emit an error on an unrecognized SDK name (PR #181897)

[Cyndy Ishida via cfe-commits]

cyndyishida wrote:

Is it a hard error because of Werror? In the test case case it looks valid to warn about this since the isysroot path is infact wrong for the given target triple.

https://github.com/llvm/llvm-project/pull/181897