This checkin basically amounts to a complete rewrite of the type-resolution

This checkin basically amounts to a complete rewrite of the type-resolution
machinery.  This dramatically simplifies how things works, removes irritating
little corner cases, and overall improves speed and reliability.

Highlights of this change are:

1. The exponential algorithm built into the code is now gone.  For example
   the time to disassemble one bytecode file from the mesa benchmark went
   from taking 12.5s to taking 0.16s.
2. The linker bugs should be dramatically reduced.  The one remaining bug
   has to do with constant handling, which I actually introduced in
   "union-find" checkins.
3. The code is much easier to follow, as a result of fewer special cases.
   It's probably also smaller.  yaay.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8842 91177308-0d34-0410-b5e6-96231b3b80d8