make: in stack traces from target commands, add the command level

A target can contain several commands, and these commands are likely to
contain the same expressions. To distinguish them, add one more line to
the stack trace, to narrow down the source of the error.

make: reduce line length in error messages

The error messages for deeply nested parse errors were hard to decipher,
due to the large amount of text. Split these messages into individual
lines, just as in the backtrace for .include files and .for loops. This
unified backtrace makes the output more uniform.

make: don't run erroneous commands in compat mode

When there is a parse or evaluation error in an expression that becomes
part of the command, don't run that command, as the result of the failed
evaluation typically contains garbage characters. Skip the remaining
commands from that target as well, as they may depend on the erroneous
command.

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: 1.4.2;
make: provide more context information for parse/evaluate errors

make: remove period from end of error messages and warnings

The majority of the existing error messages and warnings does not
include a period at the end. Follow this style consistently.

make(1): in lint mode, exit with error status on errors

Calling Parse_Error during parsing has always led to a nonzero exit
status. Calling Parse_Error later, when expanding the shell commands,
has had no effect on the exit status. Neither had calling Error.

To make make a reliable tool, it has to report errors as they occur.
Enable this strict behavior in lint mode for now. Lint mode has to be
enabled explicitly, preserving the default behavior.

make(1): in lint mode, disallow dynamic variable names in :@ modifier

This is an extremely obscure feature that hopefully nobody ever
considered using.