e11sync-static: more paralellism when building

pkgs/e11sync-static.nix

@@ -6,6 +6,7 @@
   brotli,
   findutils,
   dart-sass,
+  gawk,
 }:
 stdenv.mkDerivation {
   name = "e11sync-static";
@@ -14,6 +15,8 @@ stdenv.mkDerivation {
     python3Packages.django
     python3Packages.django-compressor
     dart-sass
+    zopfli
+    brotli
   ];
   patchPhase = ''patchShebangs --build manage.py'';
   buildPhase = ''
@@ -28,8 +31,8 @@ stdenv.mkDerivation {
         -name '*.css' -or \
         -name '*.js' -or \
         -name '*.svg' | \
-      ${findutils}/bin/xargs -P''$(${coreutils}/bin/nproc) -I{} sh -c \
+        ${gawk}/bin/awk '{print "zopfli "$0;print "brotli "$0}' | \
-        "${zopfli}/bin/zopfli {} && ${brotli}/bin/brotli {}"
+        ${findutils}/bin/xargs -P''$(${coreutils}/bin/nproc) -I{} $SHELL -c {}
   '';
   installPhase = ''mv static $out'';
 }