Improvements in -X support (#1852)

* #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.

1 files changed, 33 insertions, 0 deletions

diff --git a/tools/render-test/diagnostic-defs.h b/tools/render-test/diagnostic-defs.h
new file mode 100644
index 000000000..e48012550
--- /dev/null
+++ b/tools/render-test/diagnostic-defs.h
@@ -0,0 +1,33 @@
+//
+
+// The file is meant to be included multiple times, to produce different
+// pieces of declaration/definition code related to diagnostic messages
+//
+// Each diagnostic is declared here with:
+//
+//     DIAGNOSTIC(id, severity, name, messageFormat)
+//
+// Where `id` is the unique diagnostic ID, `severity` is the default
+// severity (from the `Severity` enum), `name` is a name used to refer
+// to this diagnostic from code, and `messageFormat` is the default
+// (non-localized) message for the diagnostic, with placeholders
+// for any arguments.
+
+#ifndef DIAGNOSTIC
+#error Need to #define DIAGNOSTIC(...) before including 
+#define DIAGNOSTIC(id, severity, name, messageFormat) /* */
+#endif
+
+//
+// -1 - Notes that decorate another diagnostic.
+//
+
+
+DIAGNOSTIC(1001, Error, expectingCommaComputeDispatch, "expected 3 comma separated integers for compute dispatch size")
+DIAGNOSTIC(1002, Error, expectingPositiveComputeDispatch, "expected 3 comma positive integers for compute dispatch size")
+DIAGNOSTIC(1003, Error, unknownSourceLanguage, "unknown source language name")
+DIAGNOSTIC(1003, Error, unknown, "unknown source language name")
+DIAGNOSTIC(1004, Error, unknownCommandLineOption, "unknown command-line option '$0'")
+DIAGNOSTIC(1005, Error, unexpectedPositionalArg, "unexpected positional arg")
+
+#undef DIAGNOSTIC