[1.38] Regression: attributes starting with `rustc` are reserved for use by the `rustc` compiler

[petrochenkov]

#63628 (comment)

attributes starting with rustc are reserved for use by the rustc compiler

./reg/select-rustc/0.1.2/beta-2019-08-13.txt:[INFO] [stdout] error[E0658]: attributes starting with `rustc` are reserved for use by the `rustc` compiler

Expected breakage from #62133, attributes of the form rustc::anything are now reserved for rustc.

[nikomatsakis]

Check-in from compiler team:

Closing as expected.