[gnome-build-meta] Try to fix gtk-vnc

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 49c849f247274d099e48fd43dc7fab9202d703d3
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Fri May 18 16:47:54 2018 -0500

    Try to fix gtk-vnc
    
    It uses -Werror by default and is incompatible with GCC 8

 elements/core-deps/gtk-vnc.bst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/elements/core-deps/gtk-vnc.bst b/elements/core-deps/gtk-vnc.bst
index b04fd03..8315eea 100644
--- a/elements/core-deps/gtk-vnc.bst
+++ b/elements/core-deps/gtk-vnc.bst
@@ -12,4 +12,4 @@ depends:
 - filename: base.bst
   junction: freedesktop-sdk.bst
 variables:
-  conf-local: --with-gtk=3.0 --enable-vala
+  conf-local: --with-gtk=3.0 --enable-vala --disable-werror