clang: add isClang passthru attribute to mirror isGNU

pkgs/development/compilers/llvm/3.3/clang.nix

@@ -29,7 +29,11 @@ stdenv.mkDerivation {
       sha256 = "15mrvw43s4frk1j49qr4v5viq68h8qlf10qs6ghd6mrsmgj5vddi";
   };
 
-  passthru = { cc = stdenv.cc.cc; gcc = gccReal; };
+  passthru = {
+    isClang = true;
+    cc = stdenv.cc.cc;
+    gcc = gccReal;
+  };
 
   meta = {
     homepage = http://clang.llvm.org/;

pkgs/development/compilers/llvm/3.4/clang.nix

@@ -34,10 +34,13 @@ stdenv.mkDerivation {
     ln -sv ${llvm}/lib/clang/${version}/lib $out/lib/clang/${version}/
   '';
 
-  passthru.cc = stdenv.cc.cc;
+  passthru = {
+    isClang = true;
+    cc = stdenv.cc.cc;
     # GCC_INSTALL_PREFIX points here, so just use it even though it may not
     # actually be a gcc
-  passthru.gcc = stdenv.cc.cc;
+    gcc = stdenv.cc.cc;
+  };
 
   enableParallelBuilding = true;
 

pkgs/development/compilers/llvm/3.5/clang.nix

@@ -39,7 +39,9 @@ in stdenv.mkDerivation {
 
   enableParallelBuilding = true;
 
-  passthru = stdenv.lib.optionalAttrs stdenv.isLinux {
+  passthru = {
+    isClang = true;
+  } // stdenv.lib.optionalAttrs stdenv.isLinux {
     inherit gcc;
   };
 

pkgs/development/compilers/llvm/3.6/clang/default.nix

@@ -40,7 +40,9 @@ in stdenv.mkDerivation {
 
   enableParallelBuilding = true;
 
-  passthru = stdenv.lib.optionalAttrs stdenv.isLinux {
+  passthru = {
+    isClang = true;
+  } // stdenv.lib.optionalAttrs stdenv.isLinux {
     inherit gcc;
   };