kboot: Implement stat(2) and fstat(2) system calls

Implement stat(2) and fstat(2) in terms of newfstatat and newfstat
system calls respectively (assume we have a compat #define when
there's no newfstat and just a regular fstat and do so for ppc).

Snag struct kstat (the Linux kernel stat(2), et al interface) from musl
and attribute properly.

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