automake: add nine to make distcheck

Will allow us to catch/prevent issues, like the one in mesa 11.2.0-rc1.

Cc: "11.1 11.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

Makefile.am

@@ -28,6 +28,7 @@ AM_DISTCHECK_CONFIGURE_FLAGS = \
 	--enable-gles1 \
 	--enable-gles2 \
 	--enable-glx-tls \
+	--enable-nine \
 	--enable-va \
 	--enable-vdpau \
 	--enable-xa \