Add initial Skylark byte code generation code.

Does not yet contain any implementation for expressions and statements
but sets up various needed mechanisms and helper classes.

--
MOS_MIGRATED_REVID=107222845
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/SkylarkShell.java b/src/test/java/com/google/devtools/build/lib/syntax/SkylarkShell.java
index 72635cb..364db10 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/SkylarkShell.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/SkylarkShell.java
@@ -81,6 +81,11 @@
   }
 
   public static void main(String[] args) {
+    if (args.length > 0 && args[0].equals("--compiler-debug")) {
+      UserDefinedFunction.enableCompiler = true;
+      UserDefinedFunction.debugCompiler = true;
+      UserDefinedFunction.debugCompilerPrintByteCode = true;
+    }
     new SkylarkShell().readEvalPrintLoop();
   }
 }