Release ghc-toolchain and ghc-platform on hackage
We should release the two recently-introduced packages on hackage
- We should, when !9263 (merged), !10903 (closed), and the fixes in !10901 (closed) land, upload ghc-toolchain to hackage.
- ghc-platform has already landed on master - we should upload it to hackage.
See also the related comment in !10696 (comment 513029) asking for ghc-platform to be uploaded ASAP.