linux: Move xmknod{at} to compat symbols

It also decouple mknod{at} from xmknod{at}.  The riscv32 ABI was added
on 2.33, so it is safe to remove the old __xmknot{at} symbols and just
provide the newer mknod{at} ones.

Checked with a build for all affected ABIs. I also checked on x86_64,
i686, powerpc, powerpc64le, sparcv9, sparc64, s390, and s390x.

Reviewed-by: Lukasz Majewski <lukma@denx.de>

sysdeps/unix/sysv/linux/mknod.c

@@ -0,0 +1,28 @@
+/* Create a special or ordinary file.  Linux version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sys/stat.h>
+#include <fcntl.h>
+
+int
+__mknod (const char *path, mode_t mode, dev_t dev)
+{
+  return __mknodat (AT_FDCWD, path, mode, dev);
+}
+libc_hidden_def (__mknod)
+weak_alias (__mknod, mknod)