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: error out on parse/evaluation errors in shell commands

The expression ${VAR:X} has an unknown modifier ':X'. Previously, this
expression errored out when the expression was evaluated at parse time,
but not when the expression was evaluated when generating the commands
to bring a target up to date. The errors were previously reported, they
didn't affect the exit status, though.

Now, errors in expressions are handled in the same way, regardless of
the time at which they are evaluated.

make: error out on the "Bad modifier" error message

Previously, the "Bad modifier" error message did not affect make's exit
status. As a side effect, this kind of error now gets more context
information.

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

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.

make: error out on parse/evaluation errors in shell commands

The expression ${VAR:X} has an unknown modifier ':X'. Previously, this
expression errored out when the expression was evaluated at parse time,
but not when the expression was evaluated when generating the commands
to bring a target up to date. The errors were previously reported, they
didn't affect the exit status, though.

Now, errors in expressions are handled in the same way, regardless of
the time at which they are evaluated.

make: error out on the "Bad modifier" error message

Previously, the "Bad modifier" error message did not affect make's exit
status. As a side effect, this kind of error now gets more context
information.

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

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.

make: error out on the "Bad modifier" error message

Previously, the "Bad modifier" error message did not affect make's exit
status. As a side effect, this kind of error now gets more context
information.

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

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.