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.

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