Fix comment.

Previous commit was confused about the case we're handling: actually,
what the patch is dealing with is platforms that have optreset, *and*
have <getopt.h>, but the latter fails to declare the former.  Because
we use a linking probe to set HAVE_INT_OPTRESET, we need to be sure we
have a declaration even if <getopt.h> doesn't think it exists.

src/include/pg_getopt.h

@@ -32,8 +32,8 @@ extern int	optopt;
 #endif   /* HAVE_GETOPT_H */
 
 /*
- * Some platforms have optreset but not <getopt.h>.  Cygwin, however,
- * doesn't like this either.
+ * Some platforms have optreset but fail to declare it in <getopt.h>, so cope.
+ * Cygwin, however, doesn't like this either.
  */
 #if defined(HAVE_INT_OPTRESET) && !defined(__CYGWIN__)
 extern int	optreset;