GMP: Further attempt to fix `x86_64-darwin' builds.

svn path=/nixpkgs/trunk/; revision=25668

pkgs/development/libraries/gmp/4.nix

@@ -16,7 +16,14 @@ stdenv.mkDerivation rec {
 
   # Prevent the build system from using sub-architecture-specific
   # instructions (e.g., SSE2 on i686).
-  preConfigure = "ln -sf configfsf.guess config.guess";
+  #
+  # This is not a problem for Apple machines, which are all alike.  In
+  # addition, `configfsf.guess' would return `i386-apple-darwin10.2.0' on
+  # `x86_64-darwin', leading to a 32-bit ABI build, which is undesirable.
+  preConfigure =
+    if !stdenv.isDarwin
+    then "ln -sf configfsf.guess config.guess"
+    else ''echo "Darwin host is `./config.guess`."'';
 
   configureFlags = (if cxx then "--enable-cxx" else "--disable-cxx") +
       staticFlags;