fetchurl on Darwin: gssSupport = false (see 9b54a00160)

I can't see a better way around the problem for now.

pkgs/development/libraries/kerberos/krb5.nix

@@ -27,7 +27,7 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ pkgconfig perl ]
     ++ optional (!libOnly) yacc
     # Provides the mig command used by the build scripts
-    ++ optional (stdenv.isDarwin && !libOnly) bootstrap_cmds;
+    ++ optional stdenv.isDarwin bootstrap_cmds;
   buildInputs = [ openssl ]
     ++ optionals (!libOnly) [ openldap libedit ];
 

pkgs/top-level/all-packages.nix

@@ -184,7 +184,10 @@ with pkgs;
 
   # `fetchurl' downloads a file from the network.
   fetchurl = import ../build-support/fetchurl {
-    inherit stdenv curl;
+    inherit stdenv;
+    # On darwin, libkrb5 needs bootstrap_cmds which would require
+    # converting many packages to fetchurl_boot to avoid evaluation cycles.
+    curl = curl.override (lib.optionalAttrs stdenv.isDarwin { gssSupport = false; });
   };
 
   fetchRepoProject = callPackage ../build-support/fetchrepoproject { };