[ScopBuilder] Report to dbgs() on SCoP bailout. NFC.

This allows to use -debug to see that a SCoP was found in ScopDetect,
but dismissed by ScopBuilder.

llvm-svn: 312113
diff --git a/polly/lib/Analysis/ScopInfo.cpp b/polly/lib/Analysis/ScopInfo.cpp
index 24ab38b..813a569 100644
--- a/polly/lib/Analysis/ScopInfo.cpp
+++ b/polly/lib/Analysis/ScopInfo.cpp
@@ -4574,6 +4574,7 @@
 }
 
 void Scop::invalidate(AssumptionKind Kind, DebugLoc Loc, BasicBlock *BB) {
+  DEBUG(dbgs() << "Invalidate SCoP because of reason " << Kind << "\n");
   addAssumption(Kind, isl_set_empty(getParamSpace().release()), Loc,
                 AS_ASSUMPTION, BB);
 }