Fix lcm-bazel warnings

[jwnimmer-tri]

Fix suppressions to avoid Clang complaints about unknown flags.

Add missing suppressions to lcm-logger.

[nosracd]

Not sure how much it matters, but it looks like the example is building with an unused variable warning. Would it make sense to disable compiler warnings in the example as well?

Overall no objections to these changes, ready to merge whenever

[jwnimmer-tri]

... it looks like the example is building with an unused variable warning. Would it make sense to disable compiler warnings in the example as well?

Yes, I can confirm that I see the warning, too.

Adding the warning suppression would not be able to inherit the copts from load("//lcm-bazel/private:copts.bzl", "WARNINGS_COPTS") (they are "private") so it would be repeating the information here again.

Instead of that, I would rather fix lcm-gen to not emit unused variables in the first place. Then, all projects can avoid the need to add the warning suppression.