Centralize getopt-related declarations in a new header file pg_getopt.h.

We used to have externs for getopt() and its API variables scattered
all over the place.  Now that we find we're going to need to tweak the
variable declarations for Cygwin, it seems like a good idea to have
just one place to tweak.

In this commit, the variables are declared "#ifndef HAVE_GETOPT_H".
That may or may not work everywhere, but we'll soon find out.

Andres Freund

contrib/pgbench/pgbench.c

@@ -40,12 +40,7 @@
 #include <ctype.h>
 #include <math.h>
 #include <signal.h>
-
-#ifndef WIN32
 #include <sys/time.h>
-#include <unistd.h>
-#endif   /* ! WIN32 */
-
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #endif
@@ -89,9 +84,6 @@ static int	pthread_create(pthread_t *thread, pthread_attr_t *attr, void *(*start
 static int	pthread_join(pthread_t th, void **thread_return);
 #endif
 
-extern char *optarg;
-extern int	optind;
-
 
 /********************************************************************
  * some configurable parameters */