Recover from typo where == is used in place of =

[Rageking8]

Given the following code: link

enum test {
    a == 1,
}

fn main() {
    let x == 2;
}

The current output is:

   Compiling playground v0.0.1 (/playground)
error: expected one of `(`, `,`, `=`, `{`, or `}`, found `==`
 --> src/main.rs:2:7
  |
2 |     a == 1,
  |       ^^ expected one of `(`, `,`, `=`, `{`, or `}`

error: expected item, found `==`
 --> src/main.rs:2:7
  |
2 |     a == 1,
  |       ^^ expected item

error: could not compile `playground` due to 2 previous errors

Ideally the output should suggest replacing the == with = where appropriate as the suggestion for incorrect usage of = in place of == already exist.

[chenyukang]

@rustbot claim