configure bug for HAVE_RES_EXTERN check

[FELLIN, JEFFREY K (JEFF)]

The code used in configure.ac to check for struct __res_state _res is an extern, can fail. I'm porting the code to UWIN, (Unix on Windows, available at http://www2.research.att.com/~gsf/download) using Microsoft Visual Studio for the cc compiler. The code in lines 3483 - 3491 should include a reference to _res, to verify the compiler doesn't ignore non-referenced variables.

I suggest line 3491 should be changed from:
Int main()  { return 0; }
To
Int main() { _res.retrans=0; return 0; }

Thank you for your consideration.

Jeff Fellin