Replace perl's use of syscall(2) with a dispatcher to libc

Replace perl's use of syscall(2) with a dispatcher to libc

This removes the ability to do direct syscalls from perl, instead calling
the appropriate libc functions.

Currently we generate the dispatcher via a perl script duing build.

requested by deraadt@

nits from espie@
education from miod@
infrastructure fixes from sthen@
many improvements and ok gkoehler@
Please commit soon.  OK bluhm@