[introspection] Make scanner happy with HB_EXTERN
diff --git a/src/Makefile.am b/src/Makefile.am
index fe14287..ec55656 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -419,6 +419,7 @@
 	-DHB_OT_H_IN \
 	-DHB_GOBJECT_H \
 	-DHB_GOBJECT_H_IN \
+	-DHB_EXTERN= \
 	$(NULL)
 HarfBuzz_0_0_gir_LIBS = \
 	libharfbuzz.la \