ifcvt: Handle multiple rewired regs and refactor noce_convert_multiple_sets

ifcvt: Handle multiple rewired regs and refactor noce_convert_multiple_sets

The existing implementation of need_cmov_or_rewire and
noce_convert_multiple_sets_1 assumes that sets are either REG or SUBREG.
This commit enchances them so they can handle/rewire arbitrary set statements.

To do that a new helper struct noce_multiple_sets_info is introduced which is
used by noce_convert_multiple_sets and its helper functions. This results in
cleaner function signatures, improved efficientcy (a number of vecs and hash
set/map are replaced with a single vec of struct) and simplicity.

gcc/ChangeLog:

	* ifcvt.cc (need_cmov_or_rewire): Renamed init_noce_multiple_sets_info.
	(init_noce_multiple_sets_info): Initialize noce_multiple_sets_info.
	(noce_convert_multiple_sets_1): Use noce_multiple_sets_info and handle
	rewiring of multiple registers.
	(noce_convert_multiple_sets): Updated to use noce_multiple_sets_info.
	* ifcvt.h (struct noce_multiple_sets_info): Introduce new struct
	noce_multiple_sets_info to store info for noce_convert_multiple_sets.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/ifcvt_multiple_sets_rewire.c: New test.