compiler.h: Do not include sys/io.h on ARM with glibc

<sys/io.h> on ARM hasn't worked for a long, long time, so it was removed
it from glibc upstream.

Remove the include to avoid a compilation failure on ARM with glibc.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Closes: https://gitlab.freedesktop.org/xorg/xserver/issues/840
(cherry picked from commit fe4cd0e7)