ghc 8.10.6: Init
Backport which adds, rather than updates, the GHC release.
----
The only big change is required for darwin since GHC 8.10.5 now
runs xattr in the install phase on darwin:
* https://gitlab.haskell.org/ghc/ghc/-/commit/11e1dcde0d3137a8ee5cd32697b2925ea4e84b95
* https://gitlab.haskell.org/ghc/ghc/-/commit/ec451cac39de919621c783fec809c26fb9f0d1c8
Unfortunately, it uses the host /usr/bin/xattr by default which is
present in the build due to a lack of sandboxing on darwin. That xattr
version however still requires Python 2.7 whereas Python 3.8 is in PATH
in our build. We solve this by setting the XATTR environment variable.
We can't use python3Packages.xattr since GHC expects Apple's fork of
xattr which provides some extra flags to utilize.
Co-authored-by: Cheng Shao <cheng.shao@tweag.io>
(Adapted from cb330ce4f05f5a6e2da3021e9cbf4ea2eb592631)
