Fix the generated gobject headers
These headers are not acceptable to modern compilers.
gcc says things like:
/usr/include/harfbuzz/hb-gobject-enums.h:100:1: warning:
function declaration isn’t a prototype [-Wstrict-prototypes]
100 | hb_gobject_ot_metrics_tag_get_type () G_GNUC_CONST;
diff --git a/src/hb-gobject-enums.h.tmpl b/src/hb-gobject-enums.h.tmpl
index a846786..6dd98f7 100644
--- a/src/hb-gobject-enums.h.tmpl
+++ b/src/hb-gobject-enums.h.tmpl
@@ -43,7 +43,7 @@
/*** BEGIN value-header ***/
HB_EXTERN GType
-@enum_name@_get_type () G_GNUC_CONST;
+@enum_name@_get_type (void) G_GNUC_CONST;
#define @ENUMPREFIX@_TYPE_@ENUMSHORT@ (@enum_name@_get_type ())
/*** END value-header ***/