[Patch] Turn -fexcess-precision=fast on when in -ffast-math

[Patch] Turn -fexcess-precision=fast on when in -ffast-math

	* common.opt (excess_precision): Tag as SetByCombined.
	* opts.c (set_fast_math_flags): Also set
	flag_excess_precision_cmdline.
	(fast_math_flags_set_p): Also check flag_excess_precision_cmdline.
	* doc/invoke.texi (-fexcess-precision): Drop text saying the
	option has no effect under -ffast-math, make it clear that
	-ffast-math will cause -fexcess-precision=fast by default even for
	standards compliant modes.
	(-ffast-math): Document that this sets -fexcess-precision=fast.

From-SVN: r243824