* #include an absolute path didn't work - because paths were taken to always be relative.

* Added SourceLoc handling for command line parsing.

* Fix typo in debug.

* Fix issue around the DiagnosticSink used in options parsing not having a writer available - by having DiagnosticSink parenting.

* Small rename for clarity.

* WIP extracting command line args for downstream tools.

* Unit tests/bug fixes around extracting args.

* Use DownstreamArgs in the EndToEndCompileRequest

* Passing downstream compiler options downstream.

* Fix issue with endToEndReq being nullptr.

* Fix issue with diagnostics number change.

* Small improvements to how the source line is displayed if it's too long.
Default to 120, as suggested in previous review.

* Make render test use x-args parsing and CommandArgReader.

* Added missing diagnostics.

* More DownstreamArgs to linkage so can be seen by 'components'.
Added dxc-x-arg test.

* Used combination of name and args instead of two Lists, which whilst equivalent was perhaps a little confusing.

* Added documentation for -X support.

* Added test for x-args parsing diagnostic. Improved diagnostic with list of known names.

* Fix issues from merge.

* Fix lookup for -matrix-layout-column-major in render test.

* Remove commented out line.