Opt compiler: Add disassembly to the '.cfg' output.

This is automatically added to the '.cfg' output when using the usual
`--dump-cfg` option.

Change-Id: I864bfc3a8299c042e72e451cc7730ad8271e4deb
diff --git a/compiler/optimizing/code_generator_x86_64.h b/compiler/optimizing/code_generator_x86_64.h
index 215754c..a18e89a 100644
--- a/compiler/optimizing/code_generator_x86_64.h
+++ b/compiler/optimizing/code_generator_x86_64.h
@@ -245,6 +245,10 @@
     return &assembler_;
   }
 
+  const X86_64Assembler& GetAssembler() const OVERRIDE {
+    return assembler_;
+  }
+
   ParallelMoveResolverX86_64* GetMoveResolver() OVERRIDE {
     return &move_resolver_;
   }