meson: Move -fsanitize=undefined into normal configuraton

meson: Move -fsanitize=undefined into normal configuraton

With 8e466dd09246 and 23ef50ae2d0c, we disable function pointer
sanitization in CI because the qemu code base does not support it.
We must disable this for normal usage of --enable-ubsan as well,
so move it there.

Append options rather than prepend, since all of this requires
proper ordering of options.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240813095216.306555-3-richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>