Add pluralise macro
Add pluralise macro

Adress issue #64238. Create a macro to be used for pluralisation check
throughout rustc codebase.

aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust