Revert r296395.

This mistakenly removed the SUBDIR_PARALLEL but even worse is that the install
(and build) order is not correct due to the lack of SUBDIR_DEPEND on the
most critical libraries. The only reason they build correctly now is because
buildworld's 'make libraries' orders them properly.

Pointyhat to: bdrewery
Sponsored by: EMC / Isilon Storage Division