[LRA]: Spill pseudos assigned to fp when fp->sp elimination became impossible

[LRA]: Spill pseudos assigned to fp when fp->sp elimination became impossible

Porting LRA to AVR revealed that creating a stack slot can make fp->sp
elimination impossible.  The previous patches undoes fp assignment after
the stack slot creation but calculated wrongly live info after this.  This
resulted in wrong generation by deleting some still alive insns.  This
patch fixes this problem.

gcc/ChangeLog:

	* lra-int.h (lra_update_fp2sp_elimination): Change the prototype.
	* lra-eliminations.cc (spill_pseudos): Record spilled pseudos.
	(lra_update_fp2sp_elimination): Ditto.
	(update_reg_eliminate): Adjust spill_pseudos call.
	* lra-spills.cc (lra_spill): Assign stack slots to pseudos spilled
	in lra_update_fp2sp_elimination.