Relax check against commuting XOR and ASHIFTRT in combine.c

Relax check against commuting XOR and ASHIFTRT in combine.c

gcc/:
	* combine.c (simplify_shift_const_1): Allow commuting (ashiftrt (xor))
	when result_mode == shift_mode.

gcc/testsuite/:
	* gcc.dg/combine_ashiftrt_1.c: New test.
	* gcc.dg/combine_ashiftrt_2.c: Likewise.
	* gcc.target/aarch64/singleton_intrinsics_1.c: Remove scan-assembler
	workarounds for cmge.
	* gcc.target/aarch64/simd/int_comparisons_1.c: Likewise; also check for
	absence of mvn.

From-SVN: r215531