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

src/port/getopt.c

@@ -32,6 +32,8 @@
 
 #include "c.h"
 
+#include "pg_getopt.h"
+
 #if defined(LIBC_SCCS) && !defined(lint)
 static char sccsid[] = "@(#)getopt.c	8.3 (Berkeley) 4/27/95";
 #endif   /* LIBC_SCCS and not lint */
@@ -49,20 +51,13 @@ int			opterr = 1,			/* if error message should be printed */
 			optind = 1,			/* index into parent argv vector */
 			optopt;				/* character checked for validity */
 char	   *optarg;				/* argument associated with option */
-#else
 
-extern int	opterr;
-extern int	optind;
-extern int	optopt;
-extern char *optarg;
 #endif
 
 #define BADCH	(int)'?'
 #define BADARG	(int)':'
 #define EMSG	""
 
-int			getopt(int nargc, char *const * nargv, const char *ostr);
-
 /*
  * getopt
  *	Parse argc/argv argument vector.