rtl-ssa: Support for creating new uses [PR113070]

rtl-ssa: Support for creating new uses [PR113070]

This exposes an interface for users to create new uses in RTL-SSA.
This is needed for updating uses after inserting a new store pair insn
in the aarch64 load/store pair fusion pass.

gcc/ChangeLog:

	PR target/113070
	* rtl-ssa/accesses.cc (function_info::create_use): New.
	* rtl-ssa/changes.cc (function_info::finalize_new_accesses):
	Ensure new uses end up referring to permanent defs.
	* rtl-ssa/functions.h (function_info::create_use): Declare.