[NFC] Rename ScopInfo to ScopBuilder

Contributed-by: Utpal Bora <cs14mtech11017@iith.ac.in>
Reviewed-by: Michael Kruse <meinersbur@googlemail.com>
               Johannes Doerfert <doerfert@cs.uni-saarland.de>

  Differential Revision: http://reviews.llvm.org/D20831

llvm-svn: 271521