E0370 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0370.rs

E0370 needs a span_label, an updated title, and a new note, changing it from:

error[E0370]: enum discriminant overflowed on value after 9223372036854775807i64; set explicitly via Y = -9223372036854775808i64 if that is desired outcome
  --> src/test/compile-fail/E0370.rs:17:5
   |
17 |     Y, //~ ERROR E0370
   |     ^ 

To:

error[E0370]: enum overflowed
  --> src/test/compile-fail/E0370.rs:17:5
   |
17 |     Y, //~ ERROR E0370
   |     ^ overflowed after 9223372036854775807i64
   |
   = note: explicitly set `Y = -9223372036854775808i64` if that is desired outcome