Fix deprecate warning "extern crate ... as ..."

Its arguments were inverted.
auto merge of #17015 : seb-m/rust/fix-extern-crate-as, r=sfackler

Its arguments were inverted.

For instance it displayed this message:

```
warning: this extern crate syntax is deprecated. Use: extern create "foobar" as foo;
```

Instead of:

```
warning: this extern crate syntax is deprecated. Use: extern create "foo" as foobar;
```