Go bindings: add DIBuilder.InsertValueAtEnd

Expose llvm::DIBuilder::insertDbgValueIntrinsic as
DIBuilder.InsertValueAtEnd in the Go bindings, to support attaching
debug metadata to register values.

Patch by Andrew Wilkins!

Differential Revision: http://reviews.llvm.org/D6374

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222790 91177308-0d34-0410-b5e6-96231b3b80d8