In our company, we add half the headwind and all the gust up to 20kts, which is added to our landing speed, which we get from the flight mgt computer. In the 737, the max crosswind landing is 35kts. We have 757s in our company too, and the max crosswind is 45kts.
We can have two warnings about windshear in the cockpit. "Caution Windshear" means you can continue, but "Windshear" is a compulsory go-around. Once done, it is just a question of how much fuel you have if you have another go, or divert.
I was chatting to a 757 captain the other day, and he told me that he had done a landing at Leeds in 45kts of x-wind with gusts over 60kts and explained it was the hardest landing he had done - right on his limit of capability. I guess that's it; if you don't feel safe, go and land somewhere else.
Last winter MAN closed due to the wind after multiple go-arounds. I was speaking to colleagues who diverted to Teeside, and they explained that when they opened the flight deck door after landing, the stench of vomit from the cabin was over-powering....