Revert "Remove support for building with LLVM 3.1"

This reverts commit d3c567503b.

Conflicts:
	opt.cpp

ctx.h

@@ -40,15 +40,20 @@
 
 #include "ispc.h"
 #include <map>
-#if defined(LLVM_3_2)
+#if defined(LLVM_3_1) || defined(LLVM_3_2)
   #include <llvm/InstrTypes.h>
   #include <llvm/Instructions.h>
 #else
   #include <llvm/IR/InstrTypes.h>
   #include <llvm/IR/Instructions.h>
 #endif
-#include <llvm/DebugInfo.h>
-#include <llvm/DIBuilder.h>
+#if defined(LLVM_3_1)
+  #include <llvm/Analysis/DebugInfo.h>
+  #include <llvm/Analysis/DIBuilder.h>
+#else
+  #include <llvm/DebugInfo.h>
+  #include <llvm/DIBuilder.h>
+#endif
 
 struct CFInfo;