add tuple_calls compiler flag for erlang 21

From http://www.erlang.org/news/123 :
* "Tuple calls" have been removed from the run-time system.

http://erlang.org/download/otp_src_21.0.readme
* OTP-14497 

               For legacy code that need to use parameterized modules
               or tuple calls for some other reason, there is a new
               compiler option called tuple_calls. When this option is
               given, the compiler will generate extra code that
               emulates the old behavior for calls where the module is
               a variable.
1 file changed