clang-stdenv: move libstdcxxHook to cc-wrapper

pkgs/development/compilers/llvm/4/default.nix

@@ -37,14 +37,17 @@ let
     llvm-manpages = lowPrio self.llvm.man;
     clang-manpages = lowPrio self.clang-unwrapped.man;
 
-    clang = wrapCC self.clang-unwrapped;
+    clang = if stdenv.cc.isGNU then self.libstdcxxClang else self.libcxxClang;
 
-    openmp = callPackage ./openmp.nix {};
+    libstdcxxClang = ccWrapperFun {
+      cc = self.clang-unwrapped;
+      /* FIXME is this right? */
+      inherit (stdenv.cc) libc nativeTools nativeLibc;
+      extraPackages = [ libstdcxxHook ];
+    };
 
     libcxxClang = ccWrapperFun {
       cc = self.clang-unwrapped;
-      isClang = true;
-      inherit (self) stdenv;
       /* FIXME is this right? */
       inherit (stdenv.cc) libc nativeTools nativeLibc;
       extraPackages = [ self.libcxx self.libcxxabi ];
@@ -53,11 +56,16 @@ let
     stdenv = stdenv.override (drv: {
       allowedRequisites = null;
       cc = self.clang;
-      # Use the gcc libstdc++ when targeting linux.
-      extraBuildInputs = if stdenv.cc.isGNU then [ libstdcxxHook ] else drv.extraBuildInputs;
+      # Don't include the libc++ and libc++abi from the original stdenv.
+      extraBuildInputs = stdenv.lib.optional stdenv.isDarwin darwin.CF;
     });
 
-    libcxxStdenv = overrideCC stdenv self.libcxxClang;
+    libcxxStdenv = stdenv.override (drv: {
+      allowedRequisites = null;
+      cc = self.libcxxClang;
+      # Don't include the libc++ and libc++abi from the original stdenv.
+      extraBuildInputs = stdenv.lib.optional stdenv.isDarwin darwin.CF;
+    });
 
     lld = callPackage ./lld.nix {};
 
@@ -66,6 +74,8 @@ let
     libcxx = callPackage ./libc++ {};
 
     libcxxabi = callPackage ./libc++abi.nix {};
+
+    openmp = callPackage ./openmp.nix {};
   };
 
 in self