revert previous; code checking tool is incorrect. Variables are not being
used in the non tbolt case.
When sanitising test output, replace "${TEST_MAKE}" with "make".
This string may appear in error messages that end up in the output.
Stricter sed expression for matching an optional PID in square brackets.
Give each group of tests its own output file.

* Rename each sub-makefile to *.mk;
* Add a *.exp file of expected output for each sub-makefile;
* Remove test.exp, which is replaced by all the other *.exp files.
* Use suffix rules to generate *.rawout and *.out files for
  each test case.
* Rewrite the test and accept targets to adapt to the new way.

The old (now removed) test.exp file is almost identical to the
concatenation (in the correct order) of all the new *.exp files.  There
are expected differences in makefile names embedded in the output, and
the new "exit status" lines.  Some old "*** Error code 1 (ignored)"
lines are also removed (replaced by new "exit status 1" lines).
#if 0 code to map the VGA BIOS
I've been unable to find any code that actually uses the mapping and we may
want to read the ROM from drm2.
If no users show up within a week or so I'll delete it.
Correct minor TX_CTRL_0_ guess and document the INTR interrupt control
register bits from the lan9730 docs. No functional change.
Fix I2C naming for HDMI
Restore ABI for fast_{u,}int_*_t to what we have used for thirteen years.
Revert previous, we have restores ABI for {u,}int_fast_*_t.
Add varmisc.mk, for miscellaneous variable tests.

For now, the only test is copied from
src/tests/usr.bin/make/d_unmatchedvarparen.mk.  This was
the only test in src/tests/usr.bin/make that was not also in
src/usr.bin/make/unit-tests.

XXX: src/tests/usr.bin/mk should be changed to reach over to
src/usr.bin/make/unit-tests, instead of keeping out of date copies
of the tests.
over-initialize for the benefit of gcc
Add a .PATH, so you can be in any other directory and run
"make -f /path/to/this/Makefile sometest.out"
and have it create sometest.out in your current directory.