After this commit there are no more bit rotted files.
The testing program that was in ir.zig has been moved to main.zig
Unsupported command line options have been deleted, or error messages
added.
The compiler repl is available from the build-exe, build-lib,
build-obj commands with the --watch option.
The main zig build script now builds the self-hosted compiler
unconditionally. Linking against LLVM is behind a -Denable-llvm
flag that defaults to off.
e1d4b59c5b