Add "const". And clean up.

Change-Id: I70e6994a0cd1d897e6981d5642108fee1324708f
diff --git a/lib/ExecutionEngine/Compiler.cpp b/lib/ExecutionEngine/Compiler.cpp
index ff7f0f1..45958dc 100644
--- a/lib/ExecutionEngine/Compiler.cpp
+++ b/lib/ExecutionEngine/Compiler.cpp
@@ -296,7 +296,7 @@
 }
 
 
-int Compiler::compile(CompilerOption &option) {
+int Compiler::compile(const CompilerOption &option) {
   llvm::Target const *Target = NULL;
   llvm::TargetData *TD = NULL;
   llvm::TargetMachine *TM = NULL;