build: update with gnulib fixes

* gnulib: Update to incorporate gnulib fixes
from Bruno Haible

diff --git a/gnulib b/gnulib
index af32ee824ee18255839f9812b8ed61aa5257a82b..259829e78b9e434771388269cd7ff3f55ce74057 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit af32ee824ee18255839f9812b8ed61aa5257a82b
+Subproject commit 259829e78b9e434771388269cd7ff3f55ce74057