travis: test out-of-tree builds

Force one config to build 'out-of-tree' (object files and executables
are created in a tree outside the project source code).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
1 file changed