Raising this to track discussion about GHC on Arm64. There is already some discussion in ticket #11206 (closed) (ARM is generally a disaster), but that ticket is about 32 bit Arm which is vastly different and is now mostly fixed. Information worth saving from #11206 (closed):

• GHC 7.8.4 from Debian can build the ghc-8.0 branch, but cannot build HEAD because HEAD requires ghc-7.10 to build.
• GHC 7.10 from Debian is broken because of an unfixed bug in llvm-3.5.2.
• ~~User @mfox reports that ghc-7.10 does build against llvm-3.7 and results in a compiler that can build HEAD.~~
• ~~That GHC 7.10 can be build against llvm-3.7 is a happy accident. Versions of GHC are usually locked to a specific version of LLVM.~~