[SPIR-V] Compile the original source with -fspv-debug instead of the -P output #9022

With -fspv-debug, dxcompilerobj.cpp compiles the output of a -P pass.

Line numbers map back through #line markers, but debug columns are positions in the preprocessed line, so they are wrong on any line that contains a macro expansion or a removed comment. spirv-val now rejects the module when a column is past the end of the original line (#8543).

I'm testing a fix for #8543 that clamps the columns and leaves them approximate.

The -P pass is also how SpirvEmitter::HandleTranslationUnit finds the included files. It lists them from the #line table the pass writes (#6935, for #6907).

Steve Urquhart (@SteveUrquhart), do you think that the include list can come from somewhere other than the #line table, for example the SourceManager file entries?