Revert "linux: Move xmknod{at} to compat symbols"

This reverts commit 81b83ff6 to move
__xmknod{at} back to default symbols.  ABIs with default symbol version
of 2.33 or newer (such as riscv32) continue to just provide the mknod*
symbols.

The idea is to not force static libraries built against old glibc
to update against new glibcs (since they reference the the
xmknod{at} symbols).

Checked on x86_64-linux-gnu and i686-linux-gnu.