[LLVM-C] Add Accessors For Global Variable Metadata Properties

[LLVM-C] Add Accessors For Global Variable Metadata Properties

Summary: Metadata for a global variable is really a  (GlobalVariable, Expression) tuple.  Allow access to these, then allow retrieving the file, scope, and line for a DIVariable, whether global or local.  This should be the last of the accessors required for uniform access to location and file information metadata.

Reviewers: jberdine, whitequark, deadalnix

Reviewed By: jberdine, whitequark

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60725

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358532 91177308-0d34-0410-b5e6-96231b3b80d8