clasp-common-lisp: use ninjaFlags instead of explicitly setting buildPhase and installPhase

pkgs/development/compilers/clasp/default.nix

@@ -59,6 +59,8 @@ stdenv.mkDerivation {
     libclang
   ];
 
+  ninjaFlags = [ "-C" "build" ];
+
   postUnpack = lib.concatStringsSep "\n" (builtins.map unpackDependency dependencies);
 
   configurePhase = ''
@@ -75,14 +77,6 @@ stdenv.mkDerivation {
       --share-path=$out/share
   '';
 
-  buildPhase = ''
-    ninja -C build
-  '';
-
-  installPhase = ''
-    ninja -C build install
-  '';
-
   meta = {
     description = "A Common Lisp implementation based on LLVM with C++ integration";
     license = lib.licenses.lgpl21Plus ;