[RISC-V][PR target/117649] Fix branch on masked values splitter

[RISC-V][PR target/117649] Fix branch on masked values splitter

Andreas reported GCC mis-compiled GAS for risc-v  Thankfully he also reduced it
to a nice little testcase.

So the whole point of the pattern in question is to "reduce" the constants by
right shifting away common unnecessary bits in RTL expressions like this:

>   [(set (pc)
>         (if_then_else (any_eq
>                     (and:ANYI (match_operand:ANYI 1 "register_operand" "r")
>                           (match_operand 2 "shifted_const_arith_operand" "i"))
>                     (match_operand 3 "shifted_const_arith_operand" "i"))
>          (label_ref (match_operand 0 "" ""))
>          (pc)))

When applicable, the reduced constants in operands 2/3 fit into a simm12 and
thus do not need multi-instruction synthesis.  Note that we have to also shift
operand 1.

That shift should have been an arithmetic shift, but was incorrectly coded as a
logical shift.

Fixed with the obvious change on the right shift opcode.

Expecting to push to the trunk once the pre-commit tester renders its verdict.
I've already tested in this my tester for rv32 and rv64.

	PR target/117649
gcc/
	* config/riscv/riscv.md (branch on masked/shifted operands): Use
	arithmetic rather than logical shift for operand 1.

gcc/testsuite

	* gcc.target/riscv/branch-1.c: Update expected output.
	* gcc.target/riscv/pr117649.c: New test.