Delete superfluous/duplicated #includes

replace ad-hoc illegal instruction with the architecturally defined one
("permanently undefined")
ok deraadt@ kettenis@

SYS___threxit cannot fail, but this integration looks like a gadget.
Put a hard-trap instruction after the syscall instruction.
ok kettenis mortimer

Use internal names for __errno, _memcpy, memset, and {,_}{set,long}jmp
Eliminate pointless use of PIC_SYM()
Split out DEFS.h from SYS.h like some other archs

ok kettenis@ deraadt@

Adds hidden _libc_FOO aliases for the system call stubs.
Stop generating _brk and _sbrk symbols: they've already been hidden.
Set the ELF symbol size on the syscall stubs.
Give the __{min,cur}brk sym

Adds hidden _libc_FOO aliases for the system call stubs.
Stop generating _brk and _sbrk symbols: they've already been hidden.
Set the ELF symbol size on the syscall stubs.
Give the __{min,cur}brk symbols a size and type, and hide more jump labels.

alpha, arm, m88k, sh, sparc, and vax assistance miod@
hppa assistance kettenis@
ok deraadt@ miod@

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__tfork() needs to set the stack address of the new thread in the kernel,
so that it can't get a signal while still running on the parent thread's
stack. Also, pass in sizeof(struct __tfork) to prov

__tfork() needs to set the stack address of the new thread in the kernel,
so that it can't get a signal while still running on the parent thread's
stack. Also, pass in sizeof(struct __tfork) to provide forward compat
when more members are added. This is an ABI change, so switch syscall
numbers and bump lib majors this time.

ok deraadt@ matthew@

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Move __tfork_thread() from rthreads (libpthread) to libc so that
it can be used for not-strictly-threading purposes

ok matthew@ kurt@