Update to latest gnulib to fix ffs() detection on mingw

ffs() was not correctly detected on mingw with previous gnulib rebase:

  https://lists.gnu.org/archive/html/bug-gnulib/2018-07/msg00061.html.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

diff --git a/.gnulib b/.gnulib
index 5b78831df03b49408676227604cf16f90dee07ac..cdbf3d385a32ff904c96f20c26f3470bd8345248 160000 (submodule)
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit 5b78831df03b49408676227604cf16f90dee07ac
+Subproject commit cdbf3d385a32ff904c96f20c26f3470bd8345248