llvmPackages: Multuple outputs for everythting

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
  db29857eb391ed002046090851a44c452b80bdbd, 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)`

1 files changed, 1 insertions, 1 deletions

diff --git a/pkgs/os-specific/darwin/maloader/default.nix b/pkgs/os-specific/darwin/maloader/default.nix
index 3943092bcf0..9142484e043 100644
--- a/pkgs/os-specific/darwin/maloader/default.nix
+++ b/pkgs/os-specific/darwin/maloader/default.nix
@@ -16,7 +16,7 @@ stdenv.mkDerivation {
       ld-mac.cc
   '';
 
-  NIX_CFLAGS_COMPILE = "-I${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = "-I${lib.getDev libcxx}/include/c++/v1";
   buildInputs = [ clang libcxx ];
   buildFlags = [ "USE_LIBCXX=1" "release" ];