[REVIEW] 16548 uts Makefiles could be much less verbose and shared between platforms

[REVIEW] 16548 uts Makefiles could be much less verbose and shared between platforms

[Richard Lowe]

These are the leaf usr/src/uts Makefile changes I floated several
months ago, and got feedback from Robert and Yuri.  These changes are
now layerd onto illumos-gate itself, and provided for real code
review.

https://code.illumos.org/c/illumos-gate/+/3477 Move sources that are
logically part of the introduction of */Makefile.com
https://code.illumos.org/c/illumos-gate/+/3478 Commonize common
aspects of the uts build
https://code.illumos.org/c/illumos-gate/+/3479 Introduce Makefile.kmod
https://code.illumos.org/c/illumos-gate/+/3480 Sort OBJS, DEPENDS_ON
in a way that breaks wsdiff

The changes are presented in order for ease of testing, and the final
number/arrangement of commits is undecided.  Input on this is also
desired.  The separate commits do stand alone (for building, etc), but
obviously aren't necessarily useful without eachother.

If you don't really care about what I did to the code, read
usr/src/uts/README.md in "Introduce Makefile.kmod" which tells you
what's different, how to write new makefiles, and what do if you want
to do as little as humanly possible instead.

If you want to see a snapshot of what this looks like with arm in the mix, see

richlowe/illumos-gate's arm64/uts-make-readme branch.

I have experimentally merged this into an illumos-omnios fork to see
what would happen.  Merging both "properly" and "lazily" was
mechanical and trivial, despite the many extra kernel bits (lx,
hyperv).

Please be gentle,

-- Rich