[LLVM-C] Add DIFile Field Accesssors

Summary:
Add accessors for the file, directory, source file name (curiously, an `Optional` value?), of a DIFile.

This is intended to replace the LLVMValueRef-based accessors used in D52239

Reviewers: whitequark, jberdine, deadalnix

Reviewed By: whitequark, jberdine

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60489

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358577 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed