(getopt) [_WIN32]: In order to prevent namespace conflict between MSC and

MinGW created an extern getopt() in unistd.h.  MinGW has getopt() in the library.
MSC does not have getopt() function.

src/lib/w32/unistd.h

@@ -38,9 +38,15 @@
 #include <stdio.h>
 #undef fileno
 #include "sys/socket.h"
-#include "getopt.h"
 #include <sys/stat.h>
 
+/*
+ * getopt.c
+ */
+extern int getopt(int, char * const[], const char *);
+extern char *optarg;
+extern int optind, opterr, optopt;
+
 /*
  * posixfile.c
  */