Summary:
gnu addr2line prints DWARF line table discriminators like so:
<file>:<line> (discriminator <Number>)
This matches that behavior.
Document how and when --output-style=GNU prints discriminators
Add test for new GNU-style discriminator printing.
Reviewers: rupprecht, labath, jhenderson
Subscribers: aprantl, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73318
