Sylvain Henry authored Jul 21, 2020 and Marge Bot committed Jul 25, 2020

Previously it was in ghc-boot so that ghc-pkg could use it. However it
wasn't necessary because ghc-pkg only uses a subset of it: reading
target arch and OS from the settings file. This is now done via
GHC.Platform.ArchOS (was called PlatformMini before).