build: update gnulib submodule to latest

Mainly for:

* dce117a sig2str: list all signals on FreeBSD >= 7
* cff4b38 acl-permissions: port to USE_ACL==0 platforms

diff --git a/gnulib b/gnulib
index 71090a2a314d9c378afd6f842abb49f60b42d4ef..350f2c6fb569f42f0a8ff47fd5b7442f24f0e658 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 71090a2a314d9c378afd6f842abb49f60b42d4ef
+Subproject commit 350f2c6fb569f42f0a8ff47fd5b7442f24f0e658