Merge `proc_macro_` expansion feature gates as `proc_macro_hygiene`#52121

Merged

bors merged 1 commit intorust-lang:masterfrom

jebrosen:macros2_feature

Oct 5, 2018

Commits on Oct 3, 2018

Merge the `proc_macro_` expansion feature gates into a single `proc_macro_hygiene` gate.
jebrosen
committed