When error from local macro, include macro def span

[estebank]

• mention -Zmacro-backtrace only for non-local macros
• include span for local macro encompassing error

[rustbot]

rustc_errors::emitter was changed

cc @Muscraft

[rustbot]

r? @adwinwhite

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[rustbot]

miri is developed in its own repository. If the Miri part of this change can be broken out, consider making this change to rust-lang/miri instead. However, if Miri needs adjusting for rustc changes, just ignore this message.

cc @rust-lang/miri

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.