Compiler: GBC fix, CFG dump enhancements

Repaired some GBC generation bit rot, fixed a syntax error in
.dot cfg file generation, enhanced cfg generation to work before
SSA renaming and added new cfg dump points.

Change-Id: Id73b479209ea4d963810f67bde0ed502ed7361d3
diff --git a/src/compiler/compiler_utility.cc b/src/compiler/compiler_utility.cc
index 2e67902..0bce17c 100644
--- a/src/compiler/compiler_utility.cc
+++ b/src/compiler/compiler_utility.cc
@@ -674,7 +674,7 @@
                bb->id);
       break;
     default:
-      snprintf(name, BLOCK_NAME_LEN, "??_%d", bb->id);
+      snprintf(name, BLOCK_NAME_LEN, "_%d", bb->id);
       break;
   }
 }