gvc: Update git submodule

This fixes make distcheck.

diff --git a/src/gvc b/src/gvc
index 40cdff2479bfff581b33906a880023106f8543b5..03894efbcd010faf53bbc6e27256d27485f721b8 160000 (submodule)
--- a/src/gvc
+++ b/src/gvc
@@ -1 +1 @@
-Subproject commit 40cdff2479bfff581b33906a880023106f8543b5
+Subproject commit 03894efbcd010faf53bbc6e27256d27485f721b8