Use PRINTOBJDIR to get the object directory of libc and use that with -I.

Add -D_REENTRANT

For cerror, allow -I../libc to allow inclusion of any assym.h, if up.

Let libposix and librt have their own version of __cerror (__posix_cerror and
__rt_cerror). This enables each library (including libc) the oppurtunity to
make its __cerror hidden and avoid being called via the PLT. No user visible
differences to no need to bump the minor number.

Implementation of processor-sets, affinity and POSIX real-time extensions.
Add schedctl(8) - a program to control scheduling of processes and threads.

Notes:
- This is supported only by SCHED_M2;
- Migration of LWP mechanism will be revisited;

Proposed on: <tech-kern>. Reviewed by: <ad>.

Add cancellation stubs in libpthread for POSIX messages queues and
asynchronous I/O.

OK by <ad>.

Implementation of POSIX message queues.

Reviewed by: <ad>, <tech-kern>

branches: 1.2.4;
We should clean the ${ASM} files, not a ${PSEUDO}, which is really "pseudo" ;)
Pointed out by <veego>.

Import of POSIX Asynchronous I/O.
Seems to be quite stable. Some work still left to do.

Please note, that syscalls are not yet MP-safe, because
of the file and vnode subsystems.

Reviewed by: <tech-kern>, <ad>