MFC r263153, r263154:

- Similar to r246614, fix panic on removing urtwn(4).  It happens because
  nodes are freed after the adapter is gone.

- Reset the bit of the R92C_MCUFWDL associated with checksum report
  before loading firmware page.  It may fix this problem:
  "urtwn0: timeout waiting for checksum report"
MFC r263107:

To avoid missing a chance to cancel thread, call _pthread_testcancel at the
beginning of _sem_timedwait.

Submitted by:	Eric van Gyzen &lt; eric at vangyzen dot net &gt;
MFC r262972:
Ignore USB keyboard driver calls from critical sections.
MFC r262676:

All callers of static method load_nvlist() in spa.c handles error case,
so there is no reason to assert that we won't hit an error.  Instead,
just return that error to caller and have the upper layer handle it.

Obtained from:	FreeNAS
Reported by:	rodrigc
Reviewed by:	Matthew Ahrens
MFC r263120:

Pull in r201021 from upstream libc++ trunk:

  Fix for PR18735 - self-assignment for map/multimap gives incorrect
  results in C++03

(Please note: that is an LLVM PR identifier, not a FreeBSD one.)

Reported by:	rakuco
MFC r259535:
The fasttrap fork handler is responsible for removing tracepoints in the
child process that were inherited from its parent. However, this should
not be done in the case of a vfork, since the fork handler ends up removing
the tracepoints from the shared vm space, and userland DTrace probes in the
parent will no longer fire as a result.

Now the child of a vfork may trigger userland DTrace probes enabled in its
parent, so modify the fasttrap probe handler to handle this case and handle
the child process in the same way that it would handle the traced process.
In particular, if once traces function foo() in a process that vforks, and
the child calls foo(), fasttrap will treat this call as having come from the
parent. This is the behaviour of the upstream code.

While here, add #ifdef guards to some code that isn't present upstream.
MFC r262325:
Print a backtrace if the SDT(9) stub gets called so that there's at least
some hope of figuring out how it happened.
MFC r262754: MFV r253848 (mm):

Update vendor/xz from v5.0 branch to post-5.0.5
MFC r262741:
Do not retry on CAM_FUNC_NOTAVAIL error, but return immediately.
Merge r263091: fix mbuf flags clash that lead to failure of operation
of IPSEC and packet filters.

PR:		kern/185876
PR:		kern/186755
MFC r263021:

  Support Last-Modified behind proxies which return UTC instead of GMT.
MFC r263105, r263106:

r263105:
  Add hyperv manual pages provided by Microsoft, formatted
  for FreeBSD standards.  Very little, if any, content was
  modified.

r263106:
  Connect the hyperv driver manuals to the build.

Sponsored by:	The FreeBSD Foundation
Merge r262747: remove extraneous ifa_ref()/ifa_free().
Merge r259562,r259566,r259638,r259645,r260124 by melifaro:

  Switch netstat -rn to use standard API for retrieving list
  of routes instead of peeking inside in-kernel radix via kget.
MFC r263079:
The auio structure is only initialized when the vnode is symlink,
avoid reading from it otherwise.
MFC r263080:
Use correct types for sizeof() in the calculations for the malloc(9) sizes.
MFC r263092:
Do not vdrop() the tmpfs vnode until it is unlocked.  The hold
reference might be the last, and then vdrop() would free the vnode.
MFC r263095:
Initialize paddr to handle the case of zero size.
MFC r258054: Update LLDB to upstream r194122 snapshot

  Inludes minor changes relative to upstream, for compatibility with
  FreeBSD's in-tree LLVM 3.3:

  - Reverted LLDB r191806, restoring use of previous API.
  - Reverted part of LLDB r189317, restoring previous enum names.
  - Work around missing LLVM r192504, using previous registerEHFrames API
    (limited functionality).
  - Removed PlatformWindows header include and init/terminate calls.

Sponsored by:	DARPA, AFRL
MFC r258094: lldb: Correct a standalone debug file path

  For a file /bin/ls with a .gnu_debuglink entry of "ls.debug" the path
  should be /usr/lib/debug/bin/ls.debug, not /usr/lib/debug/bin/ls.

  ref: https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html

  Upstream defect pr17903 (http://llvm.org/pr17903)

Sponsored by:	DARPA, AFRL