Build/test with ITC words preferred

[mkobetic]

Adds a WANT_ITC env variable that will flip the core directories in the INCLUDES change effectively switching the preference for core/itc words over arch/native words.

Make sure everything builds in this mode and where possible run core tests with it too.

Few additional changes:

• build/amforth.dep - uses the assembler to list all files that it will include during the build
• build/amforth.toc - uses build/amforth.dep to compile a "table of contents", a list of all word headers it can find in the dep files including their file/line location
• build/amforth.sal - symbol and line info from the debug_line sections of amforth.elf (useful to debug file location issues)
• build/amforth.sym - full symbol dump from amforth.elf
• debug_info target - to dump debug_info details from amforth.elf