src/Makefile.am: correct compile failure for launcher-util.c

The following error message is generated during compile
In file included from launcher-util.c:43:0:
compositor.h:35:28: fatal error: wayland-server.h: No such file or directory
 #include <wayland-server.h>

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>

src/Makefile.am

@@ -53,7 +53,7 @@ libsession_helper_la_SOURCES =			\
 	weston-launch.h				\
 	launcher-util.c				\
 	launcher-util.h
-libsession_helper_la_CFLAGS = $(GCC_CFLAGS) $(LIBDRM_CFLAGS) $(PIXMAN_CFLAGS)
+libsession_helper_la_CFLAGS = $(GCC_CFLAGS) $(LIBDRM_CFLAGS) $(PIXMAN_CFLAGS) $(COMPOSITOR_CFLAGS)
 libsession_helper_la_LIBADD = $(LIBDRM_LIBS)
 
 if ENABLE_DBUS