Fix/unify top comment in lib/Analysis/PolyhedralInfo.cpp

Change the top comment in PolyhedralInfo.cpp to use // instead of ///,
similarly to headers in other files.  This fixes the issue of copyright
line exceeding textwidth and triggering polly-check-format45 failure,
e.g. seen here:

http://lab.llvm.org:8011/builders/lldb-amd64-ninja-netbsd8/builds/18293/steps/run%20unit%20tests/logs/stdio

llvm-svn: 351808