build: update gnulib for vasnprintf fix

diff --git a/gnulib b/gnulib
index fe7e2e21b5377b4917dab35aa853c2cb81c15f93..78c0415acc2ea96febfc9d68c04d765e9d2dd20d 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit fe7e2e21b5377b4917dab35aa853c2cb81c15f93
+Subproject commit 78c0415acc2ea96febfc9d68c04d765e9d2dd20d