add another level of caching for non-local pointer queries, keeping

add another level of caching for non-local pointer queries, keeping
track of whether the CachedNonLocalPointerInfo for a block is specific
to a block.  If so, just return it without any pred scanning.  This is
good for a 6% speedup on GVN (when it uses this lookup method, which
it doesn't right now).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60695 91177308-0d34-0410-b5e6-96231b3b80d8