[clang] [feature] Add command line option to print all supported target triples

rust (`rustc --print target-list`) and zig (`zig targets`) already support this, but clang does not. Running `clang -print-targets` only prints the target architectures, not target triples.

Would be a very nice quality of life feature. Discussion: https://stackoverflow.com/questions/15036909/how-to-list-supported-target-architectures-in-clang