add header for windows

Author: maurymarkowitz

src/stdhdr.h

@@ -35,6 +35,12 @@ Boston, MA 02111-1307, USA.  */
 #include <limits.h> // gives INT_MAX
 #include <signal.h> // for sig_atomic_t and signal handling
 
+#if defined(__MINGW32__) || defined(__MINGW64__)
+  #include <io.h>
+#else
+  #include <unistd.h>
+#endif
+
 #include <time.h>   // used for TIME and DATE in main and stats
 
 #include "strng.h"  // our replacement for GLib.String