[PR98777] LRA: Use preliminary created pseudo for in LRA elimination subpass

[PR98777] LRA: Use preliminary created pseudo for in LRA elimination subpass

LRA did not extend ira_reg_equiv after generation of a pseudo in
eliminate_regs_in_insn which might results in LRA crash.  It is better not
to extend ira_reg_equiv but to use preliminary generated pseudo.  The
patch implements it.

gcc/ChangeLog:

	PR rtl-optimization/98777
	* lra-int.h (lra_pmode_pseudo): New extern.
	* lra.c (lra_pmode_pseudo): New global.
	(lra): Set it up.
	* lra-eliminations.c (eliminate_regs_in_insn): Use it.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/98777
	* gcc.target/riscv/pr98777.c: New.