forwprop: Make hilo{0,1,2} an array

Making hilo{0,1,2} an array simplifies the code in some places;
mainly the range for loop where we don't need a local array.
And the copy location becomes a loop instead.

Pushed as obvios after bootstrap/test on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (struct long_mul_summand): Change
	hilo{0,1,2} into an array.
	(long_mul_set_summand): Use a copy loop instead of written out.
	(long_mul_check_consistency): Use the array directly instead
	of a local copy of the loop for the range for loop.
	(match_long_mul_phi): Replace `hilo0` with `hilo[0]`.
	Replace `hilo1` with `hilo[1]`. Replace `hilo2` with `hilo[2]`.

Signed-off-by: Andrea Pinski <andrew.pinski@oss.qualcomm.com>