Revert commit 5b45a3d0 (CheckCompilerFlag: Match the Clang "argument
unused" output for all languages, 2023-01-23, v3.26.0-rc1~38^2).  It
broke existing projects that were silently tolerating unrelated unused
arguments in their checks for C and CXX.  For example, using
`CFLAGS=-nostdinc` or `CXXFLAGS=-nostdinc++` causes those flags to be
used when driving the linker as well, and Clang warns they are unused in
that case.

Add a test case covering the now-restored behavior.

Fixes: #24591