This patch fixes ON builds where linter is not happy with unused variables.
https://bug.oraclecorp.com/pls/bug/webbug_print.show?c_rptno=28964691

Even though it fixes specific behavior of our build environment,
it can be suitable for upstream.

--- glib-2.52.0/glib/gstring.h	2018-11-27 01:02:11.709901563 +0000
+++ glib-2.52.0/glib/gstring.h	2018-11-27 00:58:52.732310445 +0000
@@ -167,7 +167,7 @@ g_string_append_c_inline (GString *gstri
       gstring->str[gstring->len] = 0;
     }
   else
-    g_string_insert_c (gstring, -1, c);
+    (void) g_string_insert_c (gstring, -1, c);
   return gstring;
 }
 #define g_string_append_c(gstr,c)       g_string_append_c_inline (gstr, c)
--- glib-2.52.0/glib/glib-autocleanups.h	2018-11-27 01:02:26.482700505 +0000
+++ glib-2.52.0/glib/glib-autocleanups.h	2018-11-27 00:59:39.293472971 +0000
@@ -32,7 +32,7 @@ static inline void
 g_autoptr_cleanup_gstring_free (GString *string)
 {
   if (string)
-    g_string_free (string, TRUE);
+    (void) g_string_free (string, TRUE);
 }
 
 /* If adding a cleanup here, please also add a test case to
--- glib-2.52.0/gobject/gobject.h	2018-11-27 01:02:40.257225970 +0000
+++ glib-2.52.0/gobject/gobject.h	2018-11-27 01:01:12.039457270 +0000
@@ -722,7 +722,7 @@ 
     return FALSE;
 
   if (new_object != NULL)
-    g_object_ref (new_object);
+    (void) g_object_ref (new_object);
 
   *object_ptr = new_object;