lra: Avoid unfolded plus-0

lra: Avoid unfolded plus-0

While backporting another patch to an earlier release, I hit a
situation in which lra_eliminate_regs_1 would eliminate an address to:

    (plus (reg:P R) (const_int 0))

This address compared not-equal to plain:

    (reg:P R)

which caused an ICE in a later peephole2.  (The ICE showed up in
gfortran.fortran-torture/compile/pr80464.f90 on the branch but seems
to be latent on trunk.)

These unfolded PLUSes shouldn't occur in the insn stream, and later code
in the same function tried to avoid them.

gcc/
	* lra-eliminations.cc (lra_eliminate_regs_1): Use simplify_gen_binary
	rather than gen_rtx_PLUS.