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.

llvm-svn: 82491