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: NEric Blake <eblake@redhat.com>
(cherry picked from commit cdd703f4)

.gnulib @ f40e61ea

-Subproject commit a363f4ed4a0e69187c97686ac44502c49c7f4b3d
+Subproject commit f40e61ea0c4940b027aade7dd48948aa93f133a4

m4/virt-compile-warnings.m4

@@ -60,18 +60,6 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
     # gcc 4.4.6 complains this is C++ only; gcc 4.7.0 implies this from -Wall
     dontwarn="$dontwarn -Wenum-compare"
 
-    # clang rather horribly ignores unknown warning flags by
-    # default. Thus to get gl_WARN_ADD to reliably detect
-    # flags, we need to set '-Werror -Wunknown-warning-option'
-    # in CFLAGS while probing support
-    WARN_CFLAGS=
-    orig_CFLAGS="$CFLAGS"
-    gl_WARN_ADD([-Wunknown-warning-option])
-    if test -n "$WARN_CFLAGS" ; then
-        WARN_CFLAGS=
-        CFLAGS="-Werror -Wunknown-warning-option $CFLAGS"
-    fi
-
     # gcc 4.2 treats attribute(format) as an implicit attribute(nonnull),
     # which triggers spurious warnings for our usage
     AC_CACHE_CHECK([whether gcc -Wformat allows NULL strings],
@@ -197,13 +185,6 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
        dnl gl_WARN_ADD([-fstack-protector])
        gl_WARN_ADD([-fstack-protector-all])
        gl_WARN_ADD([--param=ssp-buffer-size=4])
-       dnl Even though it supports it, clang complains about
-       dnl use of --param=ssp-buffer-size=4 unless used with
-       dnl the -c arg. It doesn't like it when used with args
-       dnl that just link together .o files. Unfortunately
-       dnl we can't avoid that with automake, so we must turn
-       dnl off the following clang specific warning
-       gl_WARN_ADD([-Wno-unused-command-line-argument])
        ;;
        *-*-freebsd*)
        dnl FreeBSD ships old gcc 4.2.1 which doesn't handle
@@ -244,7 +225,4 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
       AC_DEFINE_UNQUOTED([BROKEN_GCC_WLOGICALOP], 1,
        [Define to 1 if gcc -Wlogical-op reports false positives on strchr])
     fi
-
-    # Remove stuff we set for clang
-    CFLAGS="$orig_CFLAGS"
 ])