Do the 64-bit argument swap dance, for the syscalls which require it,
unconditionaly instead of only doing it if invoked indirectly through syscall
or __syscall.

While there, tweak stack argument fetching to only perform one large copyin()
call, rather than a loop of small ones.

ok kettenis@
sometimes, the callback happens when the archive isn't opened...
fix it quickly, to be fixed better later.
Simplify man_unscope(), removing 18 lines of code, that is,
removing one function argument, one function definition,
three function invocations and two pointless assert()s.
No functional change.
Mark get{,e,res}{u,g}id() and getgroups() as NOLOCK

A little while back, guenther moved user credentials to a per-process
property, but also kept a per-thread cache that would remain stable
for the duration of a thread's system call.  These system calls now
only access the thread's cached credentials, so they're safe to run
without the kernel lock.

ok kettenis, guenther
regen