Add Tier 3 Thumb-mode targets for Armv7-A, Armv7-R and Armv8-R#150556

thejpster wants to merge 3 commits intorust-lang:mainrust-lang/rust:mainfrom

thejpster:add-thumbv7a-thumbv7r-thumbv8rthejpster/rust:add-thumbv7a-thumbv7r-thumbv8rCopy head branch name to clipboard