build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 696aa74b38f8c109c21e4c01194faab53fb4cefc..39cedf6f427350ac47118d231c05a7b73b609f89 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 696aa74b38f8c109c21e4c01194faab53fb4cefc
+Subproject commit 39cedf6f427350ac47118d231c05a7b73b609f89