Stabilize AArch64 support
Up until now GHC has been largely untested on AArch64 despite there being a non-trivial number of users relying on it. We should fix this.
There are a number of issues which need to be resolved to have defensible AArch64 support:
- (#15449 (closed)) GHC's treatment of memory ordering was woefully inadequate
- (#16776, #16784 (closed), ) A variety of linker issues
DYNAMIC_BY_DEFAULT, which would allow us to side-step above linker issues, is disabled
(#16087) The LLVM codegen seems to break the external interpreter; fixed by