deft build doesn't exit with error status on build failure

[cgay]

From Mastodon:

deft build doesn't return exit code on warnings or errors? Am I holding it wrong?

% deft build --all && echo $? && _build/bin/hello-world Mark

Build of 'hello-world' completed
…
Building targets: exe within /Use...Build of "hello-world" failed with exit status 3.
0
Reference to undefined binding "STATNAMES".
Backtrace: …

"undefined binding" is a serious warning, so yeah, exit status should definitely be non-zero. Not sure about non-serious warnings (e.g., unused variable).

There's some cruft in command-line-parser that should be cleaned up too, related to using subcommands. Check execute-subcommand and execute-command.