Use AM_CONDITIONAL. Automake knows what to distribute.
It needs to be able to navigate down the subdirs to find what
needs to be included in the tarball.

To test reliably, create a tarball and expand it into a separate
directory and build with xatracker. Distcheck will not detect
missing code when such code is configured not to build.

The content of a tarball *must* always be identical, regardless
of the configuration options used or on which platform it was configured.

Signed-off-by: Gaetan Nadon <memsize@videotron.ca>
Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>