Fix link to undefined behavior documentation

[m4salah]

The link of the undefined behavior doesn't work, I don't know if it means to go to undefined or not

[alexrp]

It should be changed to "illegal behavior" and link to: https://ziglang.org/documentation/master/#Illegal-Behavior

[m4salah]

It should be changed to "illegal behavior" and link to: ziglang.org/documentation/master#Illegal-Behavior

I thought about that, but It was different terminology, So we will keep the "Undefined Behavior" label also or change it as well to Illegal behavior?

[alexrp]

I think the change you've made here is reasonable. But @mlugg may want to take a look also.