python3Packages.cffi: use build-system/dependencies (#342042)

pkgs/development/python-modules/cffi/default.nix

@@ -57,14 +57,13 @@ else
         --replace '/usr/include/libffi' '${lib.getDev libffi}/include'
     '';
 
-    nativeBuildInputs = [
-      pkg-config
-      setuptools
-    ];
+    nativeBuildInputs = [ pkg-config ];
+
+    build-system = [ setuptools ];
 
     buildInputs = [ libffi ];
 
-    propagatedBuildInputs = [ pycparser ];
+    dependencies = [ pycparser ];
 
     # The tests use -Werror but with python3.6 clang detects some unreachable code.
     env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.cc.isClang "-Wno-unused-command-line-argument -Wno-unreachable-code -Wno-c++11-narrowing";