make(1): fix exit status in -k mode if a dependency fails

Whether in -k mode or not, the exit status tells whether all requested
targets were made or not. If a dependency could not be made, the main
target was not made as well, therefore the exit status must be nonzero
in such a case.

This part of the code lacked proper unit tests until today. The unit
test deptgt-end-fail.mk is compatible with make>=2003 at least, allowing
to compare the output over time.

In 2003, in the ok-ok-ok-ok case, "Making all from all-dep." was printed
twice in a row, for whatever reason ... (40 minutes later) ... If I had
just made the two commands for 'all' and '.END' more distinguishable.
Back in 2003, the local variables for .END had not been initialized,
instead the .END node was run with the local variables of the last
preceding node. In this case, that node was 'all', therefore ${.TARGET}
had obviously expanded to 'all'.

Somewhere in 2004, the shell commands were no longer run with the -e
flag, which resulted in the "exit status $?" line to be printed in cases
that had stopped early before.

Somewhere in 2005, the local variables for the .END node had been fixed.
The variable ${.TARGET} now had the value '.END', just as expected. In
addition, the dependencies for the .END node were made, although without
getting their proper local variables. This resulted in the output
"Making out of nothing" instead of the expected "Making end-dep out of
nothing".

Still in 2005, in the test case "all=ok all-dep=ok end=ok end-dep=ERR",
the error code of the failed 'end-dep' was first reported as "*** Error
code 1 (continuing)". To compensate for this improvement, a new bug had
been introduced. The test case "all=ok all-dep=ok end=ERR end-dep=ERR"
had properly exited with status 1 on 2005-01-01, but on 2006-01-01 it
exited with status 0, thereby ignoring errors in the .END node.

Somewhere in 2008, some of the error messages (but not all) were
directed to stderr instead of stdout. The actual output stayed the same
though.

Somewhere in 2011, the dependency of the .END node got its own local
variables, and ${.TARGET} now expanded to 'end-dep', as expected.

Somewhere in 2016, the two empty lines between the "*** Error code 1
(continuing)" and the "Stop." got compressed into a single empty line.

On 2020-12-07 (that is, today), the exit status 1 has been restored in
the error cases, after it had been wrong for at least 14 years.

make(1): in tests, move command line arguments into the test proper

make(1): switch some tests to line-buffered stdout

On Alpine Linux, the output was not in the same order as on NetBSD,
at least since bmake-20200902.

The mixture of block-buffered output from child processes and make
itself was hard to predict anyway. Switching to line-buffered stdout
improves the stability of the tests.

make(1): add tests for the -i -k -v -V -W options

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.