gvc: Update git submodule

This fixes the build.

diff --git a/src/gvc b/src/gvc
index c1f42d50e3998193b952eb3ba00fe737a263d601..40cdff2479bfff581b33906a880023106f8543b5 160000 (submodule)
--- a/src/gvc
+++ b/src/gvc
@@ -1 +1 @@
-Subproject commit c1f42d50e3998193b952eb3ba00fe737a263d601
+Subproject commit 40cdff2479bfff581b33906a880023106f8543b5