build: cliptest uses also vertex-clipping.h

Add it to the list of source files.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/Makefile.am b/Makefile.am
index 8a27d44..39af03f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -476,7 +476,10 @@
 weston_image_LDADD = libtoytoolkit.la
 weston_image_CFLAGS = $(AM_CFLAGS) $(CLIENT_CFLAGS)
 
-weston_cliptest_SOURCES = clients/cliptest.c src/vertex-clipping.c
+weston_cliptest_SOURCES =				\
+	clients/cliptest.c				\
+	src/vertex-clipping.c				\
+	src/vertex-clipping.h
 weston_cliptest_CFLAGS = $(AM_CFLAGS) $(CLIENT_CFLAGS)
 weston_cliptest_LDADD = libtoytoolkit.la