Fix gnuld error parsing false positive on make errors, false negative due to trailing \r, and false parsing of new "multiple definitions" error

[0xemgy]

Fix GNULD parsing issues:

1. Do not detect false positive make errors when using Unix Makefiles as a generator.
2. Detect "undefined reference" error with a trailing "\r".
3. Parse "multiple definitions" error correctly with the first c file as file reference, and the second file as part of the error message.

[gcampbell-msft]

These changes look fine to me, but please update the CHANGELOG to have your bug fix in the 1.21 section (just recently updated, sorry about that).

Also, please include a PR description as it helps with history.