Riven into Trundle Top...?

I would say jungle help. Riven has a much better harass pattern, and is largely immune to his pillar (given that she can just dash through/over it). She also has much higher burst. Get in with one charge of Q, auto, stun, auto, and use the remainder of your dashes to disengage. Rinse and repeat. Get your jungler to lock him down and just run through his health bar as quickly as you can, before his ultimate can have a major effect.

I don't think its an easy matchup, but there are certainly tools Riven can use to stay alive. You might not be able to kill him by yourself, but you should be able to harass well enough that both of you get your farm.

Max e, get, 45% cdr, 18-12 with the mastery for stronger shield. Build deaths dance, spam e permanently while tradeing with trundle, freewin toplane. Seriously, you can fall behind and later after finishing your early cdr build with + 10% cdr in runes into deaths dance and you should be fine.

Trundle just got nerfed hard and riven just got buffed. You should be fine

Just wait until he uses Q and his buff wears off, go in, back off. Try to fight him off his W. If he E's just Q around it or try to avoid fighting.

After 6 just get ganks.