simplify-rtx: fix riscv redundant-bitmap-2.C

simplify-rtx: fix riscv redundant-bitmap-2.C

The insn simplification expected by the test, to get a bset
instruction, has been prevented since r15-9239, because we get rotates
for bit clear and shifts for bit flip, and we don't know how to
simplify those.

Teach the rtl simplifier, at the spots where it had been extended to
handle these logical simplifications, to also handle these less
obvious negations.

for  gcc/ChangeLog

	* simplify-rtx.cc (negated_ops_p): New.
	(simplify_context::simplify_binary_operation_1): Use it.