build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 3773db6..62e51f9 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 3773db653242ab7165cd300295c27405e4f9cc79
+Subproject commit 62e51f91499a7844a9de9ee7553a79a93c80ce37