build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 90108083de31d12f30c58b6686569e1845ca9a0c..42ea6679f828a0653272a51eacf904d1f52a50df 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 90108083de31d12f30c58b6686569e1845ca9a0c
+Subproject commit 42ea6679f828a0653272a51eacf904d1f52a50df