PTRACE HARDENING: copy flags to prison in same flavor than pax.
Merge branch 'hardened/current/ptrace' of https://github.com/hardenedbsd/hardenedbsd into hardened/current/ptrace
Mention read_ahead tunables/sysctls.

MFC after:	1 month
Turns out -1 is a perfectly valid error number, ERESTART.  Remove useless
code written under assumption that it wasn't.

Sponsored by:	The FreeBSD Foundation
Merge branch 'hardened/current/ptrace' of https://github.com/hardenedbsd/hardenedbsd into hardened/current/ptrace
PTRACE HARDENING: few other clean ups. plus copy sysctl settings to jail eventually same flavor than pax.
PTRACE HARDENING: style tweaks.
Allow SUBPAGE CODE field in MODE SENSE commands.
Add a few missing llvm/clang patches, update the other ones to be able
to apply with the same patch options onto a fresh upstream llvm/clang
3.4.1 checkout, and use approximately the same header tempate for them.

MFC after:	3 days
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'freebsd/master' into hardened/current/hardening
Merge remote-tracking branch 'freebsd/master' into hardened/current/segvguard
Merge remote-tracking branch 'freebsd/master' into hardened/current/ptrace
Merge remote-tracking branch 'freebsd/master' into hardened/current/log
Merge remote-tracking branch 'freebsd/master' into hardened/current/userlandenhanced
Merge branch 'hardened/current/master' into hardened/current/unstable
Merge branch 'hardened/current/hardening' into hardened/current/unstable
Merge branch 'hardened/current/segvguard' into hardened/current/unstable
Merge branch 'hardened/current/ptrace' into hardened/current/unstable
Merge branch 'hardened/current/log' into hardened/current/unstable