libkms: build the intel backend only when needed

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
diff --git a/libkms/Makefile.am b/libkms/Makefile.am
index 449a73b..dae44e9 100644
--- a/libkms/Makefile.am
+++ b/libkms/Makefile.am
@@ -15,7 +15,6 @@
 libkms_la_SOURCES = \
 	internal.h \
 	linux.c \
-	intel.c \
 	dumb.c \
 	api.c
 
@@ -23,6 +22,10 @@
 libkms_la_SOURCES += vmwgfx.c
 endif
 
+if HAVE_INTEL
+libkms_la_SOURCES += intel.c
+endif
+
 if HAVE_NOUVEAU
 libkms_la_SOURCES += nouveau.c
 endif