Log at places we fail to compile.

Useful when diagnosing some compiler issues / limitations.

Test: test.py

Change-Id: I8759d0e78b0682b300ddcadfe02793432cab2036
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index fa580d9..ff4e9aa 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -507,6 +507,7 @@
       if (block->IsCatchBlock()) {
         // TODO: Dealing with exceptional back edges could be tricky because
         //       they only approximate the real control flow. Bail out for now.
+        VLOG(compiler) << "Not compiled: Exceptional back edges";
         return kAnalysisFailThrowCatchLoop;
       }
       block->GetLoopInformation()->Populate();