Using lzip instead of xz for distributed tarballs

Hello all, GHC is distributed as .tar.xz tarballs; I assume this is because it produces small tarballs. However, xz is ill-suited for archiving due to its lack of error recovery. Moreover, lzip produces smaller tarballs with GHC (I tested with ghc-8.8.2-x86_64-deb9-linux.tar) and decompression takes about the same amount of time. There's more information on the project page: https://www.nongnu.org/lzip/lzip.html. Cheers, Vanessa McHale