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: xorg/xserver#840
(cherry picked from commit fe4cd0e7)
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