mesa: don't install GLX files if GLX is not built
Cc: "11.2 12.0" <mesa-stable@lists.freedesktop.org> Signed-off-by:Akihiko Odaki <akihiko.odaki.4i@stu.hosei.ac.jp> [Emil Velikov: Drop guards around dri_interface.h, add stable tag] Signed-off-by:
Emil Velikov <emil.velikov@collabora.com> (cherry picked from commit 42968424)