Fixes#2432
On macOS, processes with an NSApplicationMain entrypoint do not have
access to libc argc/argv. Instead, we must use NSProcessInfo. This
commit introduces an args iterator that uses NSProcessInfo, giving us
access to the args.
This also fixes an issue where we were not properly skipping argv0 when
iterating over the args. This happened to be fine because we happened to
ignore invalid args but it introduces a config error.
