Implement the function for arm, i386, and s390x, which will use it.
Add stubs for all other backends.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
6a6d772e30