nginx: add PageSpeed module (Linux only)

pkgs/development/libraries/psol/default.nix

@@ -0,0 +1,5 @@
+{ callPackage }:
+callPackage ./generic.nix {} {
+  version = "1.11.33.4";
+  sha256  = "1jq2llp0i4666rwqnx1hs4pjlpblxivvs1jkkjzlmdbsv28jzjq8";
+}

pkgs/development/libraries/psol/generic.nix

@@ -0,0 +1,16 @@
+{ fetchzip, stdenv }:
+{ version, sha256 }:
+{ inherit version; } // fetchzip {
+  inherit sha256;
+  name   = "psol-${version}";
+  url    = "https://dl.google.com/dl/page-speed/psol/${version}.tar.gz";
+
+  meta = {
+    description = "PageSpeed Optimization Libraries";
+    homepage    = "https://developers.google.com/speed/pagespeed/psol";
+    license     = stdenv.lib.licenses.asl20;
+    # WARNING: This only works with Linux because the pre-built PSOL binary is only supplied for Linux.
+    # TODO: Build PSOL from source to support more platforms.
+    platforms   = stdenv.lib.platforms.linux;
+  };
+}