Need to pass gcc -m64 on amd64 OSX

compiler/main/DynFlags.hs

@@ -2288,8 +2288,6 @@ machdepCCOpts _dflags
       --     for "normal" programs, but it doesn't support register variable
       --     declarations.
         = ( [], ["-no-cpp-precomp"] )
-#elif x86_64_apple_darwin_TARGET
-        = ( ["-m64"], [] )
 #else
         = ( [], [] )
 #endif