* doc/invoke.texi: Document that unit-at-a-time is enabled for -O3

	* toplev.c (parse_options_and_default_flags): Enable flag_unit_at_a_time
	for -O3.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@63782 138bc75d-0d04-0410-961f-82ee72b054a4