[wasm2c] Add support for trap-handling memory sandboxing

[binji]

Most Wasm engines use the CPU's hardware memory protection to handle wasm sandboxing; since wasm32 pointers are 32-bit, we can reserve 8GiB (33-bits, 32-bit index plus 32-bit offset) of address space for each memory object. All addresses outside the valid range will trap in the OS, which then can be handled and converted into a wasm trap.

We should add support for this to wasm2c output too.

[keithw]

Done in #1442