Option to avoid per-function allocation of fast interpreter

[sasq64]

Feature

Option to make the fast interpreter not allocate so much memory;

Right now, the fast interpreter allocates close to 1000 bytes of memory for each function in the web assembly which is a lot of RAM for an embedded environment.

I would like to be able to turn avoid this, even if it means letting the code run slower.

Also because the fast interpreter can be run from read-only (flash) memory, while the slow interpreter can not, and the wasm binary must be copied into RAM.

Benefit

Reducing RAM usage.

Implementation

The big culprit is in wasm_loader_ctx_init() where the two structs BranchBlock and Const constitute allocations of 192 + 704 = 896 bytes of memory per function.

Alternatives

Alternative could be to let the slow interpreter work from read-only memory, to avoid the memory needed when copying it into RAM.