I think that it’s a parallel development. It’s unlikely to be a borrowing from some PIE descendant because

• Proto-Germanic shifted PIE *k into *h (Grimm’s Law), so the word would end as *hahha. Plus a direct descendant of the word isn’t even attested in Germanic languages [see note].
• Proto-Balto-Slavic and its descendants show a single consonant in that word, as PBS *kākā́ˀtei (see Latvian kakāt, Russian какать/kakat’). The result would be *kaka or *kakaa. (A double consonant often becomes single, but the opposite is rarely true.)

*NOTE: before someone mentions German “kacken”, it’s likely a borrowing from Latin “cacō” I shit. Now that’s some borrowed shit!