x86: support globals in files without main, fix global struct decls
x86: support "extern" variables, put them in globals symbol table
x86: update docs on self-compilation progress
x86: no longer autogenerate main() if it is absent
this is necessary if I want multifile support to ever work
x86: rewrite the old tests to have main() routines
x86: export global symbols so multifile works
x86: add basic multifile support
x86: remove "echo" cruft (a legacy of the old VM target)