build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 5aad650f4e093269e4184cb150f735f6999784d6..63983c0aac914c1a585cb6a7d0b16dc170b6ee3e 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 5aad650f4e093269e4184cb150f735f6999784d6
+Subproject commit 63983c0aac914c1a585cb6a7d0b16dc170b6ee3e