[compiler-rt] Don't detect a versioned clang test compiler as GCC

[arichardson]

I was trying to build compiler-rt with /usr/bin/clang-17 and the testsuite
failed due to the code in lit.common.cfg.py:

# GCC-ASan uses dynamic runtime by default (since config.bits is not set).
if config.compiler_id == "GNU":
    gcc_dir = os.path.dirname(config.clang)
    libasan_dir = os.path.join(gcc_dir, "..", "lib" + config.bits)
    push_dynamic_library_lookup_path(config, libasan_dir)

Fix this in two ways: First, if the test compiler matches the library
compiler, set COMPILER_RT_TEST_COMPILER_ID to CMAKE_C_COMPILER_ID. Second,
relax the regex detecting clang to allow any kind of suffix.

[thetruestblue]

Seems we expect that even when we change Compiler ID, we still expect compiler rt test compiler ID to be 'Clang', and this broke our testing. Put up a PR to restore behavior in that case: #121858