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/compilers/llvm/8/clang/default.nix

@@ -1,4 +1,5 @@
-{ lib, stdenv, fetch, cmake, libxml2, llvm, version, clang-tools-extra_src, python3, lld
+{ lib, stdenv, fetch, cmake, libxml2, libllvm, version, clang-tools-extra_src, python3
+, buildLlvmTools
 , fixDarwinDylibNames
 , enableManpages ? false
 , enablePolly ? false # TODO: get this info from llvm (passthru?)
@@ -23,18 +24,22 @@ let
       ++ lib.optional enableManpages python3.pkgs.sphinx
       ++ lib.optional stdenv.hostPlatform.isDarwin fixDarwinDylibNames;
 
-    buildInputs = [ libxml2 llvm lld ];
+    buildInputs = [ libxml2 libllvm ];
 
     cmakeFlags = [
       "-DCMAKE_CXX_FLAGS=-std=c++11"
       "-DCLANGD_BUILD_XPC=OFF"
       "-DLLVM_ENABLE_RTTI=ON"
+      "-DLLVM_CONFIG_PATH=${libllvm.dev}/bin/llvm-config${lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) "-native"}"
     ] ++ lib.optionals enableManpages [
       "-DCLANG_INCLUDE_DOCS=ON"
       "-DLLVM_ENABLE_SPHINX=ON"
       "-DSPHINX_OUTPUT_MAN=ON"
       "-DSPHINX_OUTPUT_HTML=OFF"
       "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
+    ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+      "-DLLVM_TABLEGEN_EXE=${buildLlvmTools.llvm}/bin/llvm-tblgen"
+      "-DCLANG_TABLEGEN=${buildLlvmTools.libclang.dev}/bin/clang-tblgen"
     ] ++ lib.optionals enablePolly [
       "-DWITH_POLLY=ON"
       "-DLINK_POLLY_INTO_TOOLS=ON"
@@ -42,7 +47,7 @@ let
 
     patches = [
       ./purity.patch
-      ./clang-xpc.patch
+      ./xpc.patch
       # Backport for -static-pie, which the latter touches, and which is nice in
       # its own right.
       ./static-pie.patch
@@ -53,6 +58,7 @@ let
       ./compiler-rt-baremetal.patch
       # make clang -xhip use $PATH to find executables
       ./HIP-use-PATH-8.patch
+      ./gnu-install-dirs.patch
     ];
 
     postPatch = ''
@@ -69,12 +75,12 @@ let
         --replace "NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB" FALSE
     '';
 
-    outputs = [ "out" "lib" "python" ];
+    outputs = [ "out" "lib" "dev" "python" ];
 
     # Clang expects to find LLVMgold in its own prefix
     postInstall = ''
-      if [ -e ${llvm}/lib/LLVMgold.so ]; then
-        ln -sv ${llvm}/lib/LLVMgold.so $out/lib
+      if [ -e ${libllvm.lib}/lib/LLVMgold.so ]; then
+        ln -sv ${libllvm.lib}/lib/LLVMgold.so $lib/lib
       fi
 
       ln -sv $out/bin/clang $out/bin/cpp
@@ -91,11 +97,14 @@ let
       fi
       mv $out/share/clang/*.py $python/share/clang
       rm $out/bin/c-index-test
+
+      mkdir -p $dev/bin
+      cp bin/clang-tblgen $dev/bin
     '';
 
     passthru = {
       isClang = true;
-      inherit llvm;
+      inherit libllvm;
     };
 
     meta = {