Revert commit 5b45a3d0ce (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
Cases for `CheckSource{Compiles,Runs}` and `Check{Compiler,Linker}Flag`
cover the modules with the language as a parameter, not the
language-specific modules.
