treewide: Remove usage of remaining redundant platform compatability stuff

Want to get this out of here for 18.09, so it can be deprecated
thereafter.

pkgs/tools/text/html-tidy/default.nix

@@ -1,6 +1,4 @@
-{ stdenv, fetchFromGitHub, cmake, libxslt
-, hostPlatform
-}:
+{ stdenv, fetchFromGitHub, cmake, libxslt }:
 
 stdenv.mkDerivation rec {
   name = "html-tidy-${version}";
@@ -16,7 +14,7 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ cmake libxslt/*manpage*/ ];
 
   cmakeFlags = stdenv.lib.optional
-    (hostPlatform.libc or null == "msvcrt") "-DCMAKE_SYSTEM_NAME=Windows";
+    (stdenv.hostPlatform.libc or null == "msvcrt") "-DCMAKE_SYSTEM_NAME=Windows";
 
   # ATM bin/tidy is statically linked, as upstream provides no other option yet.
   # https://github.com/htacg/tidy-html5/issues/326#issuecomment-160322107