Musl only specifies in/outb for x86/x86. Use the fallback path in case
musl is used.
This should fail compilation during the linking stage but for some reason
does not. Will do if -Werror=implicit-function-declaration is specified.
Fixed up license information.
Other small cleanups.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry-picked from fa40b85f20)
