Make empty statements visible

Reason

Readability.

Example

for (i = 0; i < max; ++i);   // BAD: the empty statement is easily overlooked
v[i] = f(v[i]);

for (auto x : v) {           // better
    // nothing
}
v[i] = f(v[i]);

Enforcement

Flag empty statements that are not blocks and don't contain comments.