Make use of dri2proto_CFLAGS when building.

Signed-off-by: James Le Cuirot <chewi@aura-online.co.uk>
Reviewed-by: Robert Morell <rmorell@nvidia.com>
Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>

src/Makefile.am

@@ -12,6 +12,8 @@ libvdpau_la_SOURCES = \
     $(DRI2_SOURCES)
 
 if DRI2
+    AM_CFLAGS += \
+        $(dri2proto_CFLAGS)
     DRI2_SOURCES = \
         mesa_dri2.c \
         mesa_dri2.h