Tighten up verifier checks. The result of an invoke instruction only

Tighten up verifier checks.  The result of an invoke instruction only
dominates the normal destination, not the exceptional dest (ie, the result
of a call is undefined on an exception)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10841 91177308-0d34-0410-b5e6-96231b3b80d8