Unblocked signals are never delivered, because we
didn't record the new mask for process_pending_signals.
Handle this with the same mechanism as sigsuspend.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220315084308.433109-5-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>