Various mingw32 fixes

* The configure script did not have an option to control the CROSS
  variable
* The windows library call CreateHardLink required an additional
  preprocessor directive
* The pointer list's len attribute has a signed type, added an
  appropriate cast
* Added a function to the configure script to determine the target
  binary extension suffix. Before, make would create a binary `pqiv`
  for windows, instead of `pqiv.exe`