Assorted fixes to make pg_upgrade build on MSVC.

* There is no chmod() on Windows.
* Must always use the 3-parameter version of open()
* There is no dynloader.h - but it also appears unnecessary on all platforms
* Don't include shlobj.h because it causes compile errors, and from what I can
  see it's not actually used. This may need to be added back for mingw
  and/or cygwin in the worst case.

contrib/pg_upgrade/check.c

@@ -427,9 +427,11 @@ create_script_for_old_cluster_deletion(migratorContext *ctx,
 
 	fclose(script);
 
+#ifndef WIN32
 	if (chmod(*deletion_script_file_name, S_IRWXU) != 0)
 		pg_log(ctx, PG_FATAL, "Could not add execute permission to file:  %s\n",
 				*deletion_script_file_name);
+#endif
 
 	check_ok(ctx);
 }