Add a test for header preprocessor guards
diff --git a/src/Makefile.am b/src/Makefile.am
index 810083a..ace7686 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -113,7 +113,9 @@
 main_LDADD = libharfbuzz.la $(HBLIBS)
 
 TESTS = \
-	check-internal-symbols.sh
+	check-header-guards.sh \
+	check-internal-symbols.sh \
+	$(NULL)
 
 if HAVE_ICU
 else