Fix/improve stack pointer detection #4036
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Stack pointer detection war currently done by finding the one global that is an
i32and initialized to a non-zero.This is unreliable, as encountered in #3995, in the worst case scenario this could lead to some pretty bad undefined behavior.
This PR tries to find the stack pointer by name first,
__stack_pointer, before falling back to the old method.Additionally, I renamed all instances of "shadow stack" to just "stack", as this was inaccurate and was previously meant to describe the fact that Wasm basically has two stacks: the user-managed stack inside the Wasm module and the other stack belonging to the Wasm engine.