[LLVM-C] DIBuilder Bindings For Variable Expressions

Summary: Add DIBuilder bindings for (global) variable expressions, variable value expressions, and debug value intrinsic insertion.

Reviewers: harlanhaskins, deadalnix, whitequark

Reviewed By: whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45979

llvm-svn: 330661