Start basic support for LLVM 2.9 bitcode writer.

Change-Id: I6a54158a32e485f506f0b991f89125b8a0e60267
diff --git a/slang_backend.h b/slang_backend.h
index 6cec9c3..052be4b 100644
--- a/slang_backend.h
+++ b/slang_backend.h
@@ -25,6 +25,7 @@
 
 #include "slang.h"
 #include "slang_pragma_recorder.h"
+#include "slang_version.h"
 
 namespace llvm {
   class formatted_raw_ostream;
@@ -80,6 +81,10 @@
 
   PragmaList *mPragmas;
 
+  virtual unsigned int getTargetAPI() const {
+    return SLANG_MAXIMUM_TARGET_API;
+  }
+
   // This handler will be invoked before Clang translates @Ctx to LLVM IR. This
   // give you an opportunity to modified the IR in AST level (scope information,
   // unoptimized IR, etc.). After the return from this method, slang will start