build: update gnulib to latest; to fix failing Solaris 5.11 test

diff --git a/gnulib b/gnulib
index a1885e2dc2a8f1c79ead4e6ceca1a53827b89048..fe7e2e21b5377b4917dab35aa853c2cb81c15f93 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit a1885e2dc2a8f1c79ead4e6ceca1a53827b89048
+Subproject commit fe7e2e21b5377b4917dab35aa853c2cb81c15f93