Use an intermediate target to associate with _SUBDIR which is marked .MAKE
this allows make -n to do tree walks as expected without
doing anything else (as intended).
Use prefix _sub. to help avoid conflict with any real target.
Put the test suite in its own tests.txz distribution file.
Force all the contents of /usr/tests to go into a separate distribution
file so that users of binary releases can easily choose to not install
Create a mechanism for providing fine-grained build order dependencies
during SUBDIR_PARALLEL builds. This augments the coarse .WAIT mechanism,
which is still useful if you've got a situation such as "almost everything
depends on A and B".
c4195049f5