[LLVM-C] Add DIBuilder Bindings For Variable Creation

Summary: Wrap LLVMDIBuilderCreateAutoVariable, LLVMDIBuilderCreateParameterVariable, LLVMDIBuilderCreateExpression, and move and correct LLVMDIBuilderInsertDeclareBefore and LLVMDIBuilderInsertDeclareAtEnd from the Go bindings to the C bindings.

Reviewers: harlanhaskins, whitequark, deadalnix

Reviewed By: harlanhaskins, whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45928

llvm-svn: 330555