maint: update to latest gnulib

The latest mingw headers on Fedora 19 fail to build with gnulib
without an update.

Meanwhile, now that upstream gnulib has better handling of -W
probing for clang, we can drop some of our own solutions in
favor of upstream; thus this reverts commit c1634100, "Correctly
detect warning flags with clang".

* .gnulib: Update to latest, for mingw and clang.

Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit cdd703f4758facf37bda891deacd561816926e75)

diff --git a/.gnulib b/.gnulib
index a363f4ed4a0e69187c97686ac44502c49c7f4b3d..f40e61ea0c4940b027aade7dd48948aa93f133a4 160000 (submodule)
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit a363f4ed4a0e69187c97686ac44502c49c7f4b3d
+Subproject commit f40e61ea0c4940b027aade7dd48948aa93f133a4