Also begin to start work on cross compilation, though that will have to
be finished later.
The patches are based on the first version of
https://reviews.llvm.org/D99484. It's very annoying to do the
back-porting but the review has uncovered nothing super major so I'm
fine sticking with what I've got.
Beyond making the outputs work, I also strove to re-sync the packages,
as they have been drifting pointlessly apart for some time.
----
Other misc notes, highly incomplete
- lvm-config-native and llvm-config are put in `dev` because they are
tools just for build time.
- Clang no longer has an lld dep. That was introduced in
db29857eb3, but if clang needs help
finding lld when it is used we should just pass it flags / put in the
resource dir. Providing it at build time increases critical path
length for no good reason.
----
A note on `nativeCC`:
`stdenv` takes tools from the previous stage, so:
1. `pkgsBuildBuild`: `(?1, x, x)`
2. `pkgsBuildBuild.stdenv.cc`: `(?0, ?1, x)`
while:
1. `pkgsBuildBuild`: `(?1, x, x)`
2. `pkgsBuildBuild.targetPackages`: `(x, x, ?2)`
3. `pkgsBuildBuild.targetPackages.stdenv.cc`: `(?1, x, x)`
The opam patch makes ocaml link dependent executables with
-L${LLVM_OCAML_EXTERNAL_LLVM_LIBDIR}. This variable was previously
undefined and as a result the linker would previously be called with
just -L which makes it ignore the next argument. This would lead strange
linking errors, like missing caml_apply2.
Despite defining this variable correctly, propagating llvm is still
necessary for linking to complete. In case ocaml-llvm is a transitive
dependency only, propagatedBuildInputs is not enough. To avoid having to
guess which version of llvm was used, we provide the right one in
passthrough.
