linux(4): Get rid of __WCLONE handling.

[dchagin]

Summary

SInce 81338031 (switch linuxulator to use the native 1:1 threads)
_WALL, _WCLONE flags are broken due to the fact that (to Linux kernel)
no distinction between processes and threads - everything is runnable
task. This allows do a weird things like waiting for a thread status
change by wait() API, unlike FreeBSD where wait() is process intended
only.

[emaste]

sys/compat/linux/linux_misc.c

1002

case typo (SInce)

2760–2761

do you have a sense of how common __WCLONE use is in various Linux applications?
(of course if it's broken we shouldn't pretend to support it - I'm just curious)

[dchagin]

sys/compat/linux/linux_misc.c

2760–2761

I haven't seen, NPTL does not use _WCLONE, however illumos implemented it (I don't know the reason or bug)

[dchagin]

comment fixed

[dchagin]

leave WLINUXCLONE define as libsysdecode mktables fails,
it uses $DSTDIR/include, not $SRCDIR to build.