Pull new version of libc++ into vendor branch.
Import new libc++.  This contains some fixes for code compiled in c++98 / c++03
mode.
Import new libc++ to vendor branch.
Vendor import of libc++ trunk r180598.
Pull new libc++ into vendor branch.
MFC @r219886.
MFC @r254374.
MFC @r255128.
Update vendor/illumos/dist and vendor-sys/illumos/dist
to 14164:dceb17481b99:

Illumos ZFS issues:
  4045 zfs write throttle & i/o scheduler performance work
Update vendor-sys/illumos/dist to 14171:98413c8cf54d:

Illumos ZFS issues:
  3954 metaslabs continue to load even after hitting zfs_mg_alloc_failure limit
  4080 zpool clear fails to clear pool
  4081 need zfs_mg_noalloc_threshold
Update vendor-sys/illumos/dist to 14172:be36a38bac3d:

Illumos ZFS issues:
  4082 zfs receive gets EFBIG from dmu_tx_hold_free()
Update vendor-sys/illumos/dist to 14176:15e9457c12ec:

Illumos ZFS issues:
  1974 pages_pp_maximum/lotsfree discrepancy leads to mlock()
       failure
Add fb_info structure definition. Drivers should fill it to give access to
framebuffer.

Sponsored by:	The FreeBSD Foundation
Add Newcons KMS driver. Based on drm_fb_helper functionality.
TODO: Should be moved to separate framebuffer interface.

Sponsored by:	The FreeBSD Foundation
Enable fill of fb_info for i915kms driver.

Sponsored by:	The FreeBSD Foundation
o Rename methods according to "consdev style".
o Add cngrab/cnungrab methods.
o Allow later console attach with termcn_cnregister().

Sponsored by:	The FreeBSD Foundation
VT want keyboard too.

Sponsored by:	The FreeBSD Foundation
o Implement history buffer.
o Join history buffer with screen buffer. Same type of things.
o Reimplement buffer as an array of rows. Make it circular, so no overflow
	tracking.
o Implement VT_PROCESS mode. Locking of VT switching by owner process.
o Add debug and deadtimer sysctls. deadtimer - defaulting to 15 seconds, time
	to wait process answer in VT_PROCESS mode, to do VT switch in case when
	process hang.
o Implement later console attach.
o Fix (partially yet) keyboard allocation.
o Add drivers priority. Disallow to replace KMS driver with VGA.
o Add ability to resize terminals.

Sponsored by:	The FreeBSD Foundation
vt_history.c is not required anymore.

Sponsored by:	The FreeBSD Foundation
Forget about vt_history.c.

Sponsored by:	The FreeBSD Foundation