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
  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)`

pkgs/development/python-modules/datatable/default.nix

@@ -39,7 +39,7 @@ buildPythonPackage rec {
   checkInputs = [ docutils pytestCheckHook ];
 
   LLVM = llvm;
-  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-isystem ${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-isystem ${lib.getDev libcxx}/include/c++/v1";
 
   pytestFlagsArray = let
     # ini file (not included in tarball) required to change python_files setting,

pkgs/development/python-modules/kiwisolver/1_1.nix

@@ -14,7 +14,7 @@ buildPythonPackage rec {
     sha256 = "53eaed412477c836e1b9522c19858a8557d6e595077830146182225613b11a75";
   };
 
-  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${lib.getDev libcxx}/include/c++/v1";
 
   # Does not include tests
   doCheck = false;

pkgs/development/python-modules/kiwisolver/default.nix

@@ -15,7 +15,7 @@ buildPythonPackage rec {
     sha256 = "950a199911a8d94683a6b10321f9345d5a3a8433ec58b217ace979e18f16e248";
   };
 
-  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${lib.getDev libcxx}/include/c++/v1";
 
   nativeBuildInputs = [
     cppy

pkgs/development/python-modules/numba/default.nix

@@ -22,7 +22,7 @@ buildPythonPackage rec {
     sha256 = "55c11d7edbba2ba715f2b56f5294cad55cfd87bff98e2627c3047c2d5cc52d16";
   };
 
-  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${lib.getDev libcxx}/include/c++/v1";
 
   propagatedBuildInputs = [ numpy llvmlite setuptools ];
   pythonImportsCheck = [ "numba" ];

pkgs/development/python-modules/pandas/2.nix

@@ -59,7 +59,7 @@ buildPythonPackage rec {
   # For OSX, we need to add a dependency on libcxx, which provides
   # `complex.h` and other libraries that pandas depends on to build.
   postPatch = lib.optionalString stdenv.isDarwin ''
-    cpp_sdk="${libcxx}/include/c++/v1";
+    cpp_sdk="${lib.getDev libcxx}/include/c++/v1";
     echo "Adding $cpp_sdk to the setup.py common_include variable"
     substituteInPlace setup.py \
       --replace "['pandas/src/klib', 'pandas/src']" \

pkgs/development/python-modules/pandas/default.nix

@@ -77,7 +77,7 @@ buildPythonPackage rec {
   # For OSX, we need to add a dependency on libcxx, which provides
   # `complex.h` and other libraries that pandas depends on to build.
   postPatch = lib.optionalString stdenv.isDarwin ''
-    cpp_sdk="${libcxx}/include/c++/v1";
+    cpp_sdk="${lib.getDev libcxx}/include/c++/v1";
     echo "Adding $cpp_sdk to the setup.py common_include variable"
     substituteInPlace setup.py \
       --replace "['pandas/src/klib', 'pandas/src']" \

pkgs/development/python-modules/py3exiv2/default.nix

@@ -13,7 +13,7 @@ buildPythonPackage rec {
   buildInputs = [ exiv2 boost ];
 
   # work around python distutils compiling C++ with $CC (see issue #26709)
-  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${libcxx}/include/c++/v1";
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${lib.getDev libcxx}/include/c++/v1";
 
   meta = with lib; {
     homepage = "https://launchpad.net/py3exiv2";