Add missing cases in TcUnify.uUnfilledVars

These missing cases dealt with unifying a meta type variable with a
skolem when the kinds match -- a pretty common case.  The missing
cases meant that instead of directly solving on the fly (which is easy
in this situation) we were generating an equality constraint viat
`utype_defer`.  This isn't *wrong*, but it's a lot less efficient than
it could be!

All this arose from investigating #5631.  This one change does this
to the compiler allocation

Before:
     821,257,552 bytes allocated in the heap
              94 MB total memory in use (0 MB lost due to fragmentation)

  MUT     time    1.54s  (  1.67s elapsed)
  GC      time    1.36s  (  1.60s elapsed)
  Total   time    2.93s  (  3.27s elapsed)

After:
     424,244,124 bytes allocated in the heap
              49 MB total memory in use (0 MB lost due to fragmentation)

  MUT     time    0.64s  (  0.89s elapsed)
  GC      time    0.83s  (  0.77s elapsed)
  Total   time    1.47s  (  1.66s elapsed)

Not bad for a 3-line change!

0 files changed, 0 insertions, 0 deletions