ScopInfo: PHI-node uses in the EntryNode with an incoming BB that is not part

          of the Region are external.

During code generation we split off the parts of the PHI nodes in the entry
block, which have incoming blocks that are not part of the region. As these
split-off PHI nodes then are external uses, we consequently also need to model
these uses in ScopInfo.

llvm-svn: 251208