Compiler - switch default for null invoke test

A while back we added a debugging option to test for a
null code address on invokes, and display a debug message
if one was encountered.  Time to turn it off by default
(it can still be enabled via compilerDebugFlags).

Change-Id: Id73596aa1f288a2d0b3ce53894b48385de712988
diff --git a/src/compiler/Frontend.cc b/src/compiler/Frontend.cc
index be3a605..880341a 100644
--- a/src/compiler/Frontend.cc
+++ b/src/compiler/Frontend.cc
@@ -33,8 +33,7 @@
      0;
 
 uint32_t compilerDebugFlags = 0 |     // Enable debug/testing modes
-     // TODO: disable all of these by default in ToT
-     (1 << kDebugDisplayMissingTargets) |
+     //(1 << kDebugDisplayMissingTargets) |
      //(1 << kDebugVerbose) |
      //(1 << kDebugDumpCFG) |
      //(1 << kDebugSlowFieldPath) |