tcg/ppc: Sync tcg_out_test and constraints

tcg/ppc: Sync tcg_out_test and constraints

Ensure the code structure is the same for matching constraints
and emitting code, lest we allow constants that cannot be
trivially tested.

Cc: qemu-stable@nongnu.org
Fixes: ad788aebbab ("tcg/ppc: Support TCG_COND_TST{EQ,NE}")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2487
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <44328324-af73-4439-9d2b-d414e0e13dd7@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>