contrib: sync dg-extract-results.sh with GCC

This syncs dg-extract-results.sh with GCC.

It contains two commits: r14-4333-g346f5991569fae and r14-9393-g64273a7e6bd8ba.

contrib/ChangeLog:
	* dg-extract-results.sh: Sync with GCC.

Approved-By: Tom Tromey <tom@tromey.com>