warnings.pl: again, don't update the timestamp unless we need to
warnings.pl: again, don't update the timestamp unless we need to

Don't update the timestamp unless we really have to do so.

Signed-off-by: H. Peter Anvin (Intel) <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm