Issue Description:

https://forums.swift.org/t/import-compiler-builtins/27869/10 for context

brentdax (JIRA User) pointed out that:
"When you run

swift myscript.swift

, arguments after the filename become arguments to the script, available in CommandLine.arguments, rather than arguments to Swift." This makes sense, but can pretty easily lead to surprising behavior.

It would be nice if when processing arguments, swift could look for potentially valid swift arguments after the filename, and provide some kind of warning. We'd probably want to avoid warning on some of the single letter flags that might be commonly used by scripts though, so this might be tricky.