Add BCCContext.

BCCContext manages the global data across the libbcc infrastructure.
This includes LLVMContext object required by materialize bitcode into
llvm::Module and LLVM compilation infrastructure.

Furthermore, BCCContext is escalated to be managed in Script instead
of in the SourceInfo.

Change-Id: I6b212a29d5144d40b6e9ca1e53b605ddc4d4541c
diff --git a/lib/ExecutionEngine/Script.h b/lib/ExecutionEngine/Script.h
index e95cf8a..4534951 100644
--- a/lib/ExecutionEngine/Script.h
+++ b/lib/ExecutionEngine/Script.h
@@ -20,6 +20,7 @@
 #include <bcc/bcc.h>
 #include "bcc_internal.h"
 
+#include "BCCContext.h"
 #include "Compiler.h"
 
 #include <llvm/Support/CodeGen.h>
@@ -59,6 +60,8 @@
 
   class Script {
   private:
+    BCCContext mContext;
+
     int mErrorCode;
 
     ScriptStatus::StatusType mStatus;