llvm 5: split out compiler-rt and remove libcxxabi dep

We already did them on non-mass-rebuild llvm 6. Also, this allows
simplifying the stdenv booting.

We were missing the libcxxabi dep in compile-rt in llvm 6, so fixed that
too.

pkgs/development/compilers/llvm/5/default.nix

@@ -14,7 +14,6 @@ let
     inherit sha256;
   };
 
-  compiler-rt_src = fetch "compiler-rt" "0ipd4jdxpczgr2w6lzrabymz6dhzj69ywmyybjjc1q397zgrvziy";
   clang-tools-extra_src = fetch "clang-tools-extra" "018b3fiwah8f8br5i26qmzh6sjvzchpn358sn8v079m49f2jldm3";
 
   # Add man output without introducing extra dependencies.
@@ -24,12 +23,19 @@ let
 
   tools = stdenv.lib.makeExtensible (tools: let
     callPackage = newScope (tools // { inherit stdenv cmake libxml2 python2 isl release_version version fetch; });
+    mkExtraBuildCommands = cc: ''
+      rsrc="$out/resource-root"
+      mkdir "$rsrc"
+      ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
+      ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
+      echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString stdenv.targetPlatform.isLinux ''
+      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '';
   in {
 
-    llvm = overrideManOutput (callPackage ./llvm.nix {
-      inherit compiler-rt_src;
-      inherit (targetLlvmLibraries) libcxxabi;
-    });
+    llvm = overrideManOutput (callPackage ./llvm.nix { });
+
     clang-unwrapped = overrideManOutput (callPackage ./clang {
       inherit clang-tools-extra_src;
     });
@@ -40,14 +46,23 @@ let
 
     clang = if stdenv.cc.isGNU then tools.libstdcxxClang else tools.libcxxClang;
 
-    libstdcxxClang = wrapCCWith {
+    libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [ libstdcxxHook ];
+      extraPackages = [
+        libstdcxxHook
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
     };
 
-    libcxxClang = wrapCCWith {
+    libcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [ targetLlvmLibraries.libcxx targetLlvmLibraries.libcxxabi ];
+      extraPackages = [
+        targetLlvmLibraries.libcxx
+        targetLlvmLibraries.libcxxabi
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
     };
 
     lld = callPackage ./lld.nix {};
@@ -59,6 +74,8 @@ let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python2 isl release_version version fetch; });
   in {
 
+    compiler-rt = callPackage ./compiler-rt.nix {};
+
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
     libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;