configure: Disable thread-safety warnings on macOS The enablement of -Wthread-safety broke compilation on macOS (if -Werror is enabled, like in our CI). Disable it there by default until the problems are resolved. Signed-off-by: Thomas Huth <thuth@redhat.com> Acked-by: Kevin Wolf <kwolf@redhat.com> Message-id: 20230301113425.286946-1-thuth@redhat.com Signed-off-by: Peter Maydell <peter.maydell@linaro.org>