Do not suggest using `-Zmacro-backtrace` for builtin macros
For macros that are implemented on the compiler, or that are annotated with `rustc_diagnostic_item`, which have arbitrary implementations from the point of view of the user and might as well be intrinsics, we do *not* mention the `-Zmacro-backtrace` flag. This includes `derive`s and standard macros like `panic!` and `format!`.
This PR adds a field to every `Span`'s `ExpnData` stating whether it comes from a builtin macro. This is determined by the macro being annotated with either `#[rustc_builtin_macro]` or `#[rustc_diagnostic_item]`. An alternative to using these attributes that already exist for other uses would be to introduce another attribute like `#[rustc_no_backtrace]` to have finer control on which macros are affected (for example, an error within `vec![]` now doesn't mention the backtrace, but one could make the case that it should). Ideally, instead of carrying this information in the `ExpnData` we'd instead try to query the `DefId` of the macro (that is already stored) to see if it is annotated in some way, but we do not have access to the `TyCtxt` from `rustc_errors`.
r? `@petrochenkov`
adea7cbc09