* Update comment on stack overflow checking
This commit moves the top-level comment in `crates/cranelift/src/lib.rs`
into the location where the global value for the stack limit is
generated. Stack overflow checking is pretty localized nowadays so
there's not much need to have it at the top of the crate and most of the
words there were just adapted to this new location.
Closes#4286
* Review comments
6778b4fce2