Don't provide llvm-gcc for 10.9 at all.
Only do %-exp on TestScript once not twice

get_script() does percent-expansion, so pass its results to
run_script() with the 'no_expand' flag (all .info *Script fields were
already done this way except for TestScript). Fixes bug reported in
than the usual '%%' protection.
don't re-check after finding match
Don't re-check after finding match of mutually-exclusive options