The earlier iterations did too much guesswork when it came to things
like stderr logging and syscall origin verification. This change will
make things more conformant to existing practices. The __pledge_mode
extension now can be configured in a better way.
There's also a new `-q` flag added to pledge.com, e.g.
o//tool/build/pledge.com -qv. ls
Is a good way to disable warnings about `tty` access attempts.
This change also fixes a bug with gettid() being incorrect after fork().
We now implement the ENOENT behavior for getauxval(). The getuid() etc.
system calls are now faster too. Plus issetugid() will work on BSDs.
