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>