tools/nolibc: don't define new syscall number

All symbols created by nolibc are also visible to user code.
Syscall constants are expected to come from the kernel headers and
should not be made up by nolibc.

Refactor the logic to avoid defining syscall numbers.
Also the new code is easier to understand.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20230917-nolibc-syscall-nr-v2-3-03863d509b9a@weissschuh.net

tools/include/nolibc/sys.h

@@ -938,11 +938,10 @@ int sys_select(int nfds, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeva
 		t.tv_nsec = timeout->tv_usec * 1000;
 	}
 	return my_syscall6(__NR_pselect6, nfds, rfds, wfds, efds, timeout ? &t : NULL, NULL);
-#elif defined(__NR__newselect) || defined(__NR_select)
-#ifndef __NR__newselect
-#define __NR__newselect __NR_select
-#endif
+#elif defined(__NR__newselect)
 	return my_syscall5(__NR__newselect, nfds, rfds, wfds, efds, timeout);
+#elif defined(__NR_select)
+	return my_syscall5(__NR_select, nfds, rfds, wfds, efds, timeout);
 #else
 	return __nolibc_enosys(__func__, nfds, rfds, wfds, efds, timeout);
 #endif