samba: enable parallel building

pkgs/servers/samba/4.x.nix

@@ -66,7 +66,8 @@ stdenv.mkDerivation rec {
     ++ optional (!enableDomainController) "--without-ad-dc"
     ++ optionals (!enableLDAP) [ "--without-ldap" "--without-ads" ];
 
-  enableParallelBuilding = true;
+  # To build in parallel.
+  buildPhase = "python buildtools/bin/waf build -j $NIX_BUILD_CORES";
 
   # Some libraries don't have /lib/samba in RPATH but need it.
   # Use find -type f -executable -exec echo {} \; -exec sh -c 'ldd {} | grep "not found"' \;