Fixed error messages in librustc/back/link.rs

Error messages cleaned in librustc/middle

Error messages cleaned in libsyntax

Error messages cleaned in libsyntax more agressively

Error messages cleaned in librustc more aggressively

Fixed affected tests

Fixed other failing tests
auto merge of #12065 : mrshu/rust/error-formating-fix, r=alexcrichton

This pull request tries to fix #12050.

I went after these wrong errors quite aggressively so it might be that I also changed some strings that are not actual errors.

Please point those out and I will update this pull request accordingly.