Netbsd: standard integer types are also defined as macros

[fdopen]

Similar to #433

[yallop]

I'd like to fix this problem, but I'm not keen on the proposed solution for two reasons: it tests for a particular platform (__NETBSD__) rather than for the availability of the C99 integer types, and it depends on the implementation details of that platform, namely the availability of types such as __uint64_t.

So how about something like the following instead, which should work anywhere that uint64_t etc. are defined as macros?

#ifdef uint64_t
  /* Use the uint64_t macro to define a new typedef */ 
  typedef uint64_t ctypes_uint64_t;    

  /* Use the new typedef to replace the macro definition */ 
# undef uint64_t
  typedef ctypes_uint64_t uint64_t;
#endif

(I realise that I've merged #433, which uses the same technique proposed here. But I'd like to switch the code from that PR over to something more like what I've described above, too.)

[fdopen]

netbsd defines uint64_t in both ways: as typdef and as macro:

#ifndef uint64_t
typedef __uint64_t      uint64_t;
#define uint64_t        __uint64_t
#endif

You will end with two typdefs for uint64_t, which is a violation of the C standard (my solution had the same problem).
I've now changed the Uint_custom_val macro. If the size instead of the type is passed around as argument, it doesn't matter, if uint64_t is a macro or not.

[yallop]

That's much neater than my suggestion. Thanks!