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/5/lldb/gnu-install-dirs.patch

@@ -0,0 +1,76 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index ada293811b3e..6c2149309f65 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -7,6 +7,8 @@ set(CMAKE_MODULE_PATH
+   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+   )
+ 
++include(GNUInstallDirs)
++
+ include(LLDBStandalone)
+ include(LLDBConfig)
+ include(AddLLDB)
+diff --git a/cmake/modules/AddLLDB.cmake b/cmake/modules/AddLLDB.cmake
+index 4c6f1efd673d..179a12b49cce 100644
+--- a/cmake/modules/AddLLDB.cmake
++++ b/cmake/modules/AddLLDB.cmake
+@@ -54,14 +54,14 @@ function(add_lldb_library name)
+         endif()
+         install(TARGETS ${name}
+           COMPONENT ${name}
+-          RUNTIME DESTINATION bin
++          RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+           LIBRARY DESTINATION ${out_dir}
+           ARCHIVE DESTINATION ${out_dir})
+       else()
+         install(TARGETS ${name}
+           COMPONENT ${name}
+-          LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
+-          ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX})
++          LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}
++          ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX})
+       endif()
+       if (NOT CMAKE_CONFIGURATION_TYPES)
+         add_custom_target(install-${name}
+@@ -126,7 +126,7 @@ function(add_lldb_executable name)
+   if(ARG_GENERATE_INSTALL AND NOT (ARG_INCLUDE_IN_FRAMEWORK AND LLDB_BUILD_FRAMEWORK ))
+     install(TARGETS ${name}
+           COMPONENT ${name}
+-          RUNTIME DESTINATION bin)
++          RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
+     if (NOT CMAKE_CONFIGURATION_TYPES)
+       add_custom_target(install-${name}
+                         DEPENDS ${name}
+diff --git a/cmake/modules/LLDBConfig.cmake b/cmake/modules/LLDBConfig.cmake
+index 726552675f47..f1f769f34446 100644
+--- a/cmake/modules/LLDBConfig.cmake
++++ b/cmake/modules/LLDBConfig.cmake
+@@ -276,7 +276,7 @@ include_directories(BEFORE
+ if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
+   install(DIRECTORY include/
+     COMPONENT lldb_headers
+-    DESTINATION include
++    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+     FILES_MATCHING
+     PATTERN "*.h"
+     PATTERN ".svn" EXCLUDE
+@@ -286,7 +286,7 @@ if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
+ 
+   install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include/
+     COMPONENT lldb_headers
+-    DESTINATION include
++    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+     FILES_MATCHING
+     PATTERN "*.h"
+     PATTERN ".svn" EXCLUDE
+diff --git a/tools/intel-mpx/CMakeLists.txt b/tools/intel-mpx/CMakeLists.txt
+index 29ba9a1cacec..30e2f9334b95 100644
+--- a/tools/intel-mpx/CMakeLists.txt
++++ b/tools/intel-mpx/CMakeLists.txt
+@@ -12,4 +12,4 @@ target_link_libraries(lldb-intel-mpxtable
+                       PUBLIC liblldb LLVMSupport)
+ 
+ install(TARGETS lldb-intel-mpxtable
+-  LIBRARY DESTINATION bin)
++  LIBRARY DESTINATION ${CMAKE_INSTALL_BINDIR})