allow passing --project to juliac

[mbauman]

My main motivation here is that it allows me to alias juliac=julia /path/to/contrib/juliac.jl and then specify juliac --proj.

[gbaraldi]

I agree with this (I'm writing a full refactor of that script that uses some pieces of PackageCompiler so I just want to make sure we want --proj as the arg)
I called mine --app-project but also not sure about it

[topolarity]

I think re-using --project is fine - juliac.jl should take care of its own project / app dependencies internally automatically if at all possible.

The alternative is that users specify both (--project=./path/to/juliac --app-project=./path/to/project/to/compile) which is too confusing IMO

[topolarity]

Not sure what the repeated x86_64-apple-darwin timeouts are about, but it must be unrelated to this change.

Thanks @mbauman !