LRA: Implement combining secondary memory reload and original insn

LRA creates secondary memory reload insns but do not try to combine it
with the original insn.  This patch implements a simple insn combining
for such cases in LRA.

        PR rtl-optimization/109052

gcc/ChangeLog:

	* lra-constraints.cc: Include hooks.h.
	(combine_reload_insn): New function.
	(lra_constraints): Call it.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr109052.c: New.