[LLVM-C] Correct The Current Debug Location Accessors
Summary: Deprecate the existing accessors for the "current debug location" of an IRBuilder. The setter could not handle being reset to NULL, and the getter would create bogus metadata if the NULL location was returned. Provide direct metadata-based accessors instead.
Reviewers: whitequark, deadalnix
Reviewed By: whitequark
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D60484