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(1): error out on misspelled directives

Before, make accepted misspellings like .warnings, .export-literally and
a few others, all of which are unlikely to occur in practice. See the
test directive-misspellings.mk for further details.

make(1): add test for misspelled directives

This test allows the other directive-* tests to focus on the purpose of
the individual directive, allowing these tests to continue after
parsing, without errors.