Produces the address to which the function containing the built-in
  call will return as a 64-bit integer (on Alpha systems, the value
  of R26 on entry to the function; on I64 systems, the value of B0 on
  entry to the function).

  This built-in function cannot be used within a function specified
  to use nonstandard linkage.

  Syntax:

       __int64 __RETURN_ADDRESS (void);