make: do not compile stuff in the 'test' directory
To be consistent with the rest of the project's behaviour, do not try to
compile what is in the toplevel's "test" directory for a normal
compilation.
The content of this directory does not really test anything, so it is not
useful for users, and there is always the risk that it could break
compilation because it is not heavily maintained (and does not deserves to)
so this patch just skips the directory, as already done for wrlib/tests/
and WINGs/Tests.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>