Fix PR5023: The instruction form of DominatorTree::dominates did not

Fix PR5023: The instruction form of DominatorTree::dominates did not
take into consideration that the result of an invoke is only valid in
the normal dest, not the unwind dest.  This caused 'PHINode::hasConstantValue'
to return true in an invalid situation, causing mem2reg to delete a phi that
was actually needed.  This caused a crash building 483.xalancbmk.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82491 91177308-0d34-0410-b5e6-96231b3b80d8