message: Change how the macro "N" is undef'ed wrt clang 6 fix
  This ensures N is left untouched after abi_generator.hpp is included
diff: #include <eosio/chain/contracts/types.hpp>
  #include <fc/io/json.hpp>
  -//clashes with something deep in the AST includes
  +//clashes with something deep in the AST includes in clang 6 and possibly other versions of clang
  +#pragma push_macro("N")
  #undef N
  #include "clang/Driver/Options.h"
  @@ -228,3 +229,5 @@ namespace eosio {
  };
  } //ns eosio
  +
  +#pragma pop_macro("N")
  \ No newline at end of file
  