[Refactor] Change the comment style to silence -Wcomment

-Wcomment complained about a "multi-line comment" caused by the
  ascii art used in ScopHelper to describe the CFG.

Differential Revision: http://reviews.llvm.org/D5618

llvm-svn: 219207

polly/lib/Support/ScopHelper.cpp

@@ -123,8 +123,8 @@ BasicBlock *polly::simplifyRegion(Scop *S, Pass *P) {
     // inserted __after__ EntryBB causing the following situation:
     //
     // EnteringBB
-    //     |
-    //    / \
+    //    _|_
+    //    | |
     //    |  \-> some_other_BB_not_in_R
     //    V
     // EntryBB