[LRA]: When assigning stack slots to pseudos previously assigned to fp...

[LRA]: When assigning stack slots to pseudos previously assigned to fp consider other spilled pseudos

The previous LRA patch can assign slot of conflicting pseudos to
pseudos spilled after prohibiting fp->sp elimination.  This patch
fixes this problem.

gcc/ChangeLog:

	* lra-spills.cc (assign_stack_slot_num_and_sort_pseudos): Moving
	slots_num initialization from here ...
	(lra_spill): ... to here before the 1st call of
	assign_stack_slot_num_and_sort_pseudos.  Add the 2nd call after
	fp->sp elimination.