Following legacy packing conventions, `isArm` was defined just for
32-bit ARM instruction set. This is confusing to non packagers though,
because Aarch64 is an ARM instruction set.
The official ARM overview for ARMv8[1] is surprisingly not confusing,
given the overall state of affairs for ARM naming conventions, and
offers us a solution. It divides the nomenclature into three levels:
```
ISA: ARMv8 {-A, -R, -M}
/ \
Mode: Aarch32 Aarch64
| / \
Encoding: A64 A32 T32
```
At the top is the overall v8 instruction set archicture. Second are the
two modes, defined by bitwidth but differing in other semantics too, and
buttom are the encodings, (hopefully?) isomorphic if they encode the
same mode.
The 32 bit encodings are mostly backwards compatible with previous
non-Thumb and Thumb encodings, and if so we can pun the mode names to
instead mean "sets of compatable or isomorphic encodings", and then
voilà we have nice names for 32-bit and 64-bit arm instruction sets
which do not use the word ARM so as to not confused either laymen or
experienced ARM packages.
[1]: https://developer.arm.com/products/architecture/a-profile
These are taken from https://phabricator.haskell.org/D4388 (which is
against HEAD) and fix an inconsistency when building profiling
libraries on multiple machines that leads to linking failure.
Cabal2nix expects a --compiler flag that contains a Cabal Compiler description.
We used to use the compiler's derivation name for this, but this breaks when
cross-compiling due to the target suffix. Instead we add an explicit
haskellCompilerName attribute to Haskell compiler derivations.
GHC currently handles this stuff in a quite non-standard way, basically
taking prog var `FOO` to mean `FOO_FROM_TARGET`. It's because it
(wrongly) thinks from stage 2's perspective.
