meson: Split --enable-sanitizers to --enable-{asan, ubsan}

meson: Split --enable-sanitizers to --enable-{asan, ubsan}

We do not always want both address and undefined behavior
sanitizers running at the same time.

For the gitlab custom-runners, drop to only --enable-ubsan.
These jobs are not run by default, but as will be obvious in the
next patch, we don't run ASan on x86 either, and it seems wrong
to hold aarch64 and s390x to a different standard.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240813095216.306555-2-richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>