suitable clang stdenv

pkgs/development/libraries/gmp/5.1.x.nix

@@ -16,10 +16,13 @@ stdenv.mkDerivation (rec {
     # Build a "fat binary", with routines for several sub-architectures
     # (x86), except on Solaris where some tests crash with "Memory fault".
     # See <http://hydra.nixos.org/build/2760931>, for instance.
+    #
+    # no darwin because gmp uses ASM that clang doesn't like
     optional (!stdenv.isSunOS) "--enable-fat"
     ++ (if cxx then [ "--enable-cxx"  ]
                else [ "--disable-cxx" ])
     ++ optional (cxx && stdenv.isDarwin) "CPPFLAGS=-fexceptions"
+    ++ optional stdenv.isDarwin "ABI=64 CC=clang"
     ++ optional stdenv.is64bit "--with-pic"
     ;