wasm-backend: initial stack position doesn't take into account data+bss size

[sbc100]

Under the wasm backend we are setting the stack position using --initial-stack-pointer argument to wasm-emscripten-finalize. The value we pass is calculated based on STATIC_BUMP, but STACK_BUMP is set from the output of wasm-emscripten-finalize. This means that static data and bss effectively end up occupying the end (low addresses) of the stack.

Given a small stack and a large data/bss section the stack would overlaps completely with the static data!