Enable parallel building for ocaml-4.08 and above. tested as:
$ nix build -f. ocaml-ng.ocamlPackages_{4_{00_1,01_0,02,03,04,05,06,07,08,09,10,11,12,13},latest}.ocaml --keep-going
ocaml build system supports parallel building, but but for multiple
top-level targets at the same time as it usually spawns subprocess
$(MAKE) that occasionally conflict with one another. To work it around
we use tiny Makefile with a single rule that calls top-level targets
sequentially as makefile calls:
nixpkgs_world_bootstrap_world_opt:
$(MAKE) world
$(MAKE) bootstrap
$(MAKE) world.opt
On a 16-core machine ocaml-4.12 build speeds up from 6m55s to 1m35s.
Releases 4_00_1, 4_01_0, 4_04 and 4_05 still have some race in them.
Thus this change enables parallel builds only for ocaml-4.06 and above.
Adapted from #142723
upstreams's CI tests the parallel makefile: https://github.com/ocaml/ocaml/issues/10235#issuecomment-782100584
The limit was chosen to be 4.08 because it was released in 2019, not too
long before the above link.
The configure program for OCaml has been using a new set of command-line
arguments from version 4.08. This is a small refactoring to ease dealing with
the two sets.
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
