[PR97978] LRA: Permit temporary allocation incorrectness after hard reg split.

LRA can crash when a hard register was split and the same hard register
was assigned on the previous assignment sub-pass.  The following
patch fixes this problem.

gcc/ChangeLog:

	PR rtl-optimization/97978
	* lra-int.h (lra_hard_reg_split_p): New external.
	* lra.c (lra_hard_reg_split_p): New global.
	(lra): Set up lra_hard_reg_split_p after splitting a hard reg.
	* lra-assigns.c (lra_assign): Don't check allocation correctness
	after hard reg splitting.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/97978
	* gcc.target/i386/pr97978.c: New.