build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 0883405cc751858a633bebc56acb75381a6e50c8..b5104eb4ff3b34f51ffd22d83e45477f134361e4 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 0883405cc751858a633bebc56acb75381a6e50c8
+Subproject commit b5104eb4ff3b34f51ffd22d83e45477f134361e4