build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index d91a0d2dc678afe8a2c696077f0640e6874f52bc..0906b5f3d776d1a91b4c1f2c244cb01b2c6aabcd 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit d91a0d2dc678afe8a2c696077f0640e6874f52bc
+Subproject commit 0906b5f3d776d1a91b4c1f2c244cb01b2c6aabcd