FreeBSD_HEAD_i386 - Build #1418 - Fixed

FreeBSD_HEAD_i386 - Build #1418 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/1418/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/1418/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/1418/console

Change summaries:

289433 by bdrewery:
Correct a bitrotted comment about installworld order requirements.

The case of make(1) using a new /bin/sh issue was fixed in r173219 when ITOOLS
was introduced.

There are still issues with mid-install errors leaving a system unusable that
are currently non-trivial to solve.  The safest ordering requires installing
rtld, libc and libthr (in that order) before anything else.  We don't do that
now though.  Much improvement is needed here still.

Discussed with:	kip and kan (rtld/library ordering)
MFC after:	1 week
Sponsored by:	EMC / Isilon Storage Division

289432 by bdrewery:
Tweak the guard more to suggest 'all' if SUBDIR_OVERRIDE is specified.  In that
case 'all' does make sense.

MFC after:	2 weeks
X-MFC-With:	r289411
Sponsored by:	EMC / Isilon Storage Division

289430 by bdrewery:
Remove .MAKE from targets that do more than just run sub-makes, such as
calling rm or mtree.

MFC after:	1 week
Sponsored by:	EMC / Isilon Storage Division

289429 by scottl:
Revert an extra hunk that crept into the last commit.

Submitted by:	emax
Obtained from:	Netflix, Inc.
MFC after:	3 days