build: update gnulib submodule to latest

Fixes a false test failure with MALLOC_CHECK_ set.

* gnulib: Update to latest.

diff --git a/gnulib b/gnulib
index c499a3c497de473fd6a2ee78a76402b8846cac8a..1a72950760b1fce763ff834de0d545caab8a983c 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit c499a3c497de473fd6a2ee78a76402b8846cac8a
+Subproject commit 1a72950760b1fce763ff834de0d545caab8a983c