XY-question frame challenge.
The only way to win the game is to not play.
If you were to be jumping in, then the other answers give insightful food for thought. But that's a huge, colossal if, especially given your use case. So here comes the party-pooper...
As long as you are even moderately well prepared I would be willing to bet a lot of money that the odds of "I'm in a The Great Outdoors survival situation where I need to jump 100 feet off a cliff into water" are very slim. I think you're more likely to get struck by lightning on a clear day where no signs of lightning were present (supposedly, that happens).
Originally I was much stronger in my wording. But thanks to @BlackThorn for pointing out there are use cases similar enough to what the question asks for that they should also be seriously considered. BlackThorn wrote:
Fire on a cruise ship, fire on an aircraft carrier, friend falls off
of cliff and you want to rescue him before he drowns (and you jump
because you are confident you can survive the fall to rescue him). The
last example literally happened to a friend of mine with an 80 foot
cliff and he saved his life, holding his friends face above the water
until paramedics arrived.
Even if there is a fire on a ship, that doesn't mean you're likely to be forced to jump from the top, but that could be a possibility. If you are on a tall ship and concerned about fire safety, a safer strategy would be to review the ship's fire evacuation routes and procedures. In case of fire, a smart evacuation is better than a frantic high jump.
In the case of a friend falling from a cliff, again, that does not automatically mean someone should immediately jump in after them, especially if you don't know the safety situation at the bottom. In all emergency rescue situations, you need to ensure your own safety as well otherwise you endanger both yourself and the other person.
If a friend falls from a cliff, do not immediately jump over after them. As quickly as you can, scan the bottom for safety hazards. Wait a second to see what is happening to the person who fell as well.
I am happy for BlackThorn's friend that the outcome was favorable. However, this anecdotal evidence does not mean you should throw logic to the wind, and hopefully the heroic friend performed the rescue safely.
An 80 to 100 foot fall takes between 2-3 seconds according to a quick Google query. Human reaction time means that a rescuer is likely to be at least a second or two behind to begin with. At that point you might as well wait the 1 second to see how the victim lands since they might not even need rescuing. And if you are wearing any very cumbersome clothing you should remove it first: I know some of my boots would make it impossible to perform a water rescue in, so taking even 10 seconds to remove them would be better than jumping in with them on.
So work quickly to save the person, but don't rush to the point of making the situation worse. The old "hurry up and wait."
It has also happened that people jumping from heights into water have landed on a person at the bottom and killed them. It would be a tragic accident if a heroic effort to save someone who would not have died anyway led to both the victim and the hero dying together in vain.
If you are absolutely sure that this is actually necessary, then jump in like a rigid vertical pencil.
Realistic possibility of survival jump
The "jump off a cliff to survive" trope is exciting but not realistic.
Maybe this question was inspired by a scene I've heard about where Bear Grylls supposedly did something similar and made some people thing it was a reasonable survival tactic. I haven't seen the scene myself.
This use case is simply not realistic and is a dangerous view of wilderness survival. Even if you create a highly contrived scenario where you make it seem like this is the best option, I would still take my chances sitting tight and doing my best on the high ground. Your survival odds are likely higher.
Even if you are severely dehydrated and need the water at the bottom of the cliff, in that case I still might stay up top. To be so dehydrated that you would risk the jump means you're probably also so dehydrated that you 1) aren't thinking as clearly and are more likely to make bad choices, and 2) lack the coordination and strength to perform the jump technique well and will have even higher odds of severe injury or death.
"I still want to prepare for this rare situation anyway!"
Ok, then here's what you can do that will benefit you way more. An ounce of prevention is worth a pound of cure.
Predators: To deal with predators bring defenses and learn to use them. Bear spray, knowledge of local predators and how to remain safe around them, defensible positions (ie: don't put yourself between a cliff and predator to begin with).
Forest fire: You might still be at risk at the bottom of the cliff. You might also make it harder for rescuers to find or reach you by making such a change to your location.
Wilderness Survival: Everyone needs to get the idea out of their head that such risky actions are a part of real wilderness survival training. If you're in a wilderness survival situation, you need to avoid such risks at all costs.
Out of all the rare cases where you might otherwise be tempted to jump, in most of them you would probably be better served by bringing bear spray and bringing an emergency locator beacon to signal for help and let rescuers know your location.
Climbed up a rock face and dropped your gear? Activate your beacon. Realize a forest fire is nearby? Activate your beacon. Being hunted or attacked? Active your bear spray. Any other situation where you don't have to jump right this second? Active your beacon.
"But what if the beacon fails?" That's possible, sure, but what are the odds that will happen coinciding with an animal attack coinciding with a cliff-you-animal sandwich, coinciding with survivable water at the bottom of it? Not convinced? Get a second beacon as a back up.
Think ahead for situation-specific emergency backups, like an emergency waist pack with an extra rope and/or beacon. Similarly, if this is a concern plan for it before a trip where you're around cliffs: What could go wrong, and how could I mitigate that so I wouldn't have to jump?
Don't jump! Just bring defenses and a beacon and plan ahead, as mitigating the situation beforehand has much higher chance of success than dealing with it after.
If you do somehow manage to have no choice at all but to jump, and you decide to jump despite your terrible luck at this point, then look to the other answers and pencil drop in straight and rigid.