[OpenMP] Add Passing in Original Declaration Names To Mapper API

[OpenMP] Add Passing in Original Declaration Names To Mapper API

Summary:
This patch adds support for passing in the original delcaration name in the source file to the libomptarget runtime. This will allow the runtime to provide more intelligent debugging messages. This patch takes the original expression parsed from the OpenMP map / update clause and provides a textual representation if it was explicitly mapped, otherwise it takes the name of the variable declaration as a fallback. The information in passed to the runtime in a global array of strings that matches the existing ident_t source location strings using ";name;filename;column;row;;"

Reviewers: jdoerfert

Differential Revision: https://reviews.llvm.org/D89802