Guide: Fix inconsistency in 'Marcos' section

The old version switched in between examples from the value `5i` to `"Hello"`
and back. Additionally, the code generated by `rustc print.rs
--pretty=expanded` is not as verbose anymore.
auto merge of #17843 : coffeejunk/rust/guide-macros, r=steveklabnik

The old version switched in between examples from the value `5i` to `"Hello"` and back.

Additionally, the code generated by `rustc print.rs --pretty=expanded` is not as verbose anymore.