make: show realistic invalid line in error message

Previously, the error message 'Invalid line' showed only the expanded
line, which might or might not show the actual problem. To be more
helpful, add the unexpanded line to the error message in case they
differ.

Remove the special handling of invalid lines that result from merge
conflicts. RCS is not commonly used anymore, and mentioning CVS was too
specific. By echoing the whole line, the patterns '<<<<<<' and '>>>>>>'
are clear enough to hint at the problem.

make: add more details to error message about invalid lines

tests/make: force line-based diagnostics to be listed in the tests

This way, contradictions between the intended output and the actual
output are closer together and have a better chance of being spotted.

make: fix out-of-bounds read when parsing an invalid line

Reported by Robert Morris in https://bugs.freebsd.org/265119.

Since 2021-12-14.

tests/make: add a few more tests

tests/make: extend tests for parsing makefiles

tests/make: force line-based diagnostics to be listed in the tests

This way, contradictions between the intended output and the actual
output are closer together and have a better chance of being spotted.

make: fix out-of-bounds read when parsing an invalid line

Reported by Robert Morris in https://bugs.freebsd.org/265119.

Since 2021-12-14.

tests/make: add a few more tests

tests/make: extend tests for parsing makefiles

make: fix out-of-bounds read when parsing an invalid line

Reported by Robert Morris in https://bugs.freebsd.org/265119.

Since 2021-12-14.

tests/make: add a few more tests

tests/make: extend tests for parsing makefiles

tests/make: add a few more tests

tests/make: extend tests for parsing makefiles

tests/make: extend tests for parsing makefiles