Undo the special treatment that GHC 7.8 received and DONT rely on its built-in primops.
Instead, temporarily duplicate the foreign primops in primops.cmm, porting them to
the changed CMM syntax in 7.8.

Verified that in this state the test results on GHC 7.8.2 are the same as with the builtin
primops.  In particular, Issue #28 still fails.

Next step is to eliminate primops entirely, moving to doing everything directly in C,
cutting out the middle man.