tests/lint: test more cases of type mismatch in '?:'

branches: 1.8.2;
lint: since C99, a non-void function must return a value

lint: warn about function definitions without header declaration

The existing warning was only issued for function declarations, not for
function definitions.

The interesting change in the tests is in msg_351.c. Many other tests
use non-static functions due to their syntactic brevity. In these
tests, the warning is disabled individually, to allow new functions to
be added without generating warning 351.

tests/lint: make expectation lines in the tests more detailed

This commit migrates msg_100 until msg_199.

tests/lint: one comment per expected diagnostic

This makes it possible to check for diagnostics that contain commas.

tests/lint: keep messages in test files in sync with actual messages

Each of the tests named msg_*.c repeats the template of the message, to
make the test somewhat self-contained when viewed in isolation.

This creates a redundancy, and keeping track of this manually is next to
impossible. I tried it and failed in 9 cases, even though it has just
been 2 months since I myself created the initial files and I knew all
the time that this redundancy exists.

Be fool-proof for the future by checking this automatically.

lint: add expections to tests

msg_098: fix suffix for floating point constant
msg_127: remove prototype
msg_146: fix return type

lint: add tests for several messages

lint: add a test for each message produced by lint1

Having a test for each message ensures that upcoming refactorings don't
break the basic functionality. Adding the tests will also discover
previously unknown bugs in lint.

The tests ensure that every lint message can actually be triggered, and
they demonstrate how to do so. Having a separate file for each test
leaves enough space for documenting historical anecdotes, rationale or
edge cases, keeping them away from the source code.

The interesting details of this commit are in Makefile and
t_integration.sh. All other files are just auto-generated.

When running the tests as part of ATF, they are packed together as a
single test case. Conceptually, it would have been better to have each
test as a separate test case, but ATF quickly becomes very slow as soon
as a test program defines too many test cases, and 50 is already too
many. The time complexity is O(n^2), not O(n) as one would expect.
It's the same problem as in tests/usr.bin/make, which has over 300 test
cases as well.