configure: Allow builds with extra warnings

configure: Allow builds with extra warnings

The clang compiler supports a useful compiler option -Weverything,
and GCC also has other warnings not enabled by -Wall.

If glib header files trigger a warning, however, testing glib with
-Werror will always fail. A size mismatch is also detected without
-Werror, so simply remove it.

Cc: qemu-stable@nongnu.org
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-Id: <1461879221-13338-1-git-send-email-sw@weilnetz.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 5919e0328b7d6a08a661c3c747bae3e841d4e6f4)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>