CI / Test the different build options LIBCORO_xyz

[Dirk O. Kaar]

Using async coroutines on embedded systems, Zephyr OS in particular since it's build system is cmake based which makes integrating libcoro very natural, the options should be considered during tests. In the minimum, this set is being used and should always remain functional for new revisions of libcoro:

LIBCORO_BUILD_EXAMPLES OFF
LIBCORO_FEATURE_THREADING OFF
LIBCORO_FEATURE_NETWORKING OFF
LIBCORO_FEATURE_SSL OFF

Perhaps testing with LIBCORO_FEATURE_THREADING ON could prove useful, too.