Add "const". And clean up.

Change-Id: I70e6994a0cd1d897e6981d5642108fee1324708f
diff --git a/lib/ExecutionEngine/Compiler.h b/lib/ExecutionEngine/Compiler.h
index f436df0..b99588a 100644
--- a/lib/ExecutionEngine/Compiler.h
+++ b/lib/ExecutionEngine/Compiler.h
@@ -153,7 +153,7 @@
 
     int linkModule(llvm::Module *module);
 
-    int compile(CompilerOption &option);
+    int compile(const CompilerOption &option);
 
     char const *getErrorMessage() {
       return mError.c_str();