This function is unused, except to implement gdb_do_syscall.
Fold the implementations together.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-27-richard.henderson@linaro.org>