meson: Warn when TCI is selected but TCG backend is available

meson: Warn when TCI is selected but TCG backend is available

Some new users get confused with 'TCG' and 'TCI', and enable TCI
support expecting to enable TCG.

Emit a warning when native TCG backend is available on the
host architecture, mentioning this is a suboptimal configuration.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Suggested-by: Daniel Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210125144530.2837481-5-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>