bug#55905: warn about misplaced or duplicated doc strings, `declare` or `interactive` forms

[dick]

Ha, I considered that but the marginal cost of symbols-with-positions
conflicts wasn't sufficiently high to introduce `#define BASE_EQ EQ`.

We knew it'd be a tough sell to OG devs to turn their backs on GNU, but
we had to try.

So long as non-free software exists, we shall continue the fight (since
our operations rely on such non-free software).