[PR98722] LRA: Check that target has no 3-op add insn to transform 2 plus expression.

[PR98722] LRA: Check that target has no 3-op add insn to transform 2 plus expression.

Patch cf2ac1c30af0fa783c8d72e527904dda5d8cc330 for solving PR97969 was
assumed for targets with absent 3-op add insn.  But the original patch did
not check this.  This patch adds the check.

gcc/ChangeLog:

	PR rtl-optimization/98722
	* lra-eliminations.c (eliminate_regs_in_insn): Check that target
	has no 3-op add insn to transform insns containing two pluses.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/98722
	* g++.target/s390/pr98722.C: New.