Fix error reporting after ioctl() call with pg_upgrade --clone

errno was not reported correctly after attempting to clone a file,
leading to incorrect error reports.  While scanning through the code, I
have not noticed any similar mistakes.

Error introduced in 3a769d82.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20220731134135.GY15006@telsasoft.com
Backpatch-through: 12

src/bin/pg_upgrade/file.c

@@ -57,9 +57,11 @@ cloneFile(const char *src, const char *dst,
 
 	if (ioctl(dest_fd, FICLONE, src_fd) < 0)
 	{
+		int			save_errno = errno;
+
 		unlink(dst);
 		pg_fatal("error while cloning relation \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
-				 schemaName, relName, src, dst, strerror(errno));
+				 schemaName, relName, src, dst, strerror(save_errno));
 	}
 
 	close(src_fd);