Fix non-affine generated entering node not being recognized as dominating

Scalar reloads in the generated entering block were not recognized as
dominating the subregions locks when there were multiple entering
nodes. This resulted in values defined in there not being copied.

As a fix, we unconditionally add the BBMap of the generated entering
node to the generated entry. This fixes part of llvm.org/PR25439.

This reverts 252449 and reapplies r252445. Its test was failing
indeterministically due to r252375 which was reverted in r252522.

llvm-svn: 252540