[PR97969] LRA: Transform pattern `plus (plus (hard reg, const), pseudo)` after elimin...

[PR97969] LRA: Transform pattern `plus (plus (hard reg, const),	pseudo)` after elimination

LRA can loop infinitely on targets without `reg + imm` insns.  Register elimination
on such targets can increase register pressure resulting in permanent
stack size increase and changing elimination offset.  To avoid such situation, a simple
transformation can be done to avoid register pressure increase after
generating reload insns containing eliminated hard regs.

gcc/ChangeLog:

	PR target/97969
	* lra-eliminations.c (eliminate_regs_in_insn): Add transformation
	of pattern 'plus (plus (hard reg, const), pseudo)'.

gcc/testsuite/ChangeLog:

	PR target/97969
	* gcc.target/arm/pr97969.c: New.