Minor LLVM cleanup.

Change-Id: Ic3e88d5e551d0ee440231ce8bb515ecd31517fe2
diff --git a/src/compiler/llvm/compiler_llvm.h b/src/compiler/llvm/compiler_llvm.h
index cbee115..31973a4 100644
--- a/src/compiler/llvm/compiler_llvm.h
+++ b/src/compiler/llvm/compiler_llvm.h
@@ -89,9 +89,9 @@
  private:
   LlvmCompilationUnit* AllocateCompilationUnit();
 
-  CompilerDriver* compiler_driver_;
+  CompilerDriver* const compiler_driver_;
 
-  InstructionSet insn_set_;
+  const InstructionSet insn_set_;
 
   Mutex next_cunit_id_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
   size_t next_cunit_id_ GUARDED_BY(next_cunit_id_lock_);