Reland Implement _ExtInt as an extended int type specifier.

I fixed the LLDB issue, so re-applying the patch.

This reverts commit a4b88c044980337bb14390be654fe76864aa60ec.
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
index 4915e19..34164fb 100644
--- a/clang/lib/CodeGen/CGDebugInfo.h
+++ b/clang/lib/CodeGen/CGDebugInfo.h
@@ -168,6 +168,7 @@
   llvm::DIType *CreateType(const BuiltinType *Ty);
   llvm::DIType *CreateType(const ComplexType *Ty);
   llvm::DIType *CreateType(const AutoType *Ty);
+  llvm::DIType *CreateType(const ExtIntType *Ty);
   llvm::DIType *CreateQualifiedType(QualType Ty, llvm::DIFile *Fg);
   llvm::DIType *CreateType(const TypedefType *Ty, llvm::DIFile *Fg);
   llvm::DIType *CreateType(const TemplateSpecializationType *Ty,