C++: Set clang_version to the default from previous frontend version
C++: Set clang_version to the default from previous frontend version

This ensures that `__atomic_fetch_min` parses and that the number of
builtins does not changed compared to the previous version of the
frontend.

github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql