make: add program name to stack traces from sub-makes

make: add quotes to "in directory" line in stack traces

The other lines in stack traces use quotes as well.

make: use '"filename" line 123' for locations instead of 'filename:123'

The format 'filename:123' is commonly used for identifying a location in
a file. Text editors recognize it and allow quick navigation through it.
The previous format was specific to make and would have required custom
support in editors.

The new format was already used in stack traces, except for the first
line. Now all lines use the same format.

make: on error, print the targets to be made

This helps to understand situations with several nested sub-makes in
varying directories.

make: add more context information to error messages

In case of a parse error or evaluation error, print the variable value
in addition to the variable name, to see the effects of previous
expression modifiers.

In nested make calls, print the current directory at the bottom of a
stack trace, as that information is otherwise hard to get in a parallel
build spanning multiple directories.

branches: 1.8.2;
make: exit immediately after reading a null byte from a makefile

The chance of other garbage bytes in such a file is just too high.

make(1): re-add improved assertion in ParseGetLine

make(1): fix assertion failure for files without trailing newline

Previously, mmapped files didn't always have the final newline added.
Only those that ended at a page boundary did.

This confused ParseRawLine, which assumed (and since parse.c 1.510 from
moments ago also asserted) that every line ends with a newline, which
allows the code to assume that after a backslash, there is at least one
other character in the buffer, thereby preventing an out-of-bounds read.

This bug had been there at least since parse.c 1.170 from 2010-12-25
04:57:07, maybe even earlier, I didn't check.

Now line_end always points to the trailing newline, which allows
ParseGetLine to overwrite that character to end the string.

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): error out on null bytes in makefiles

Makefiles are text files, they must not contain null bytes.

The previous code in this area was rotten anyway. It assumed that
buf_end could be NULL even if buf_ptr was a valid pointer, which is no
longer true, probably since a few years already.

Continuing parsing after a null byte does not make sense. If there's a
null byte in a text file, that file is corrupted, and parsing it leads
to unintended effects easily. Therefore the only sensible action is to
stop parsing immediately.

The check whether cf->readMore could be null was outdated as well, which
previously made the fatal error impossible to reach. Because of the
missing unit tests, nobody noticed this though.

The "exit status 0" in opt-file.exp is worring but that's due to another
bug and will be fixed in a follow-up commit.

make(1): add test for makefile containing null bytes

make(1): test parsing a makefile that ends in a backslash

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.