message: initalize sbrk_bytes based on initial memory size of wasm memory
  sbrk_bytes needs to be initialized to the end of initial memory. Hardcoding it to 64KB means it'll stomp on any inital memory above 64KB.
diff: @@ -28,8 +28,8 @@ struct wasm_cache::entry {
  struct wasm_context {
  wasm_context(wasm_cache::entry &code, apply_context& ctx) : code(code), context(ctx)
  {
  - //initialize to minimum bytes and limit this to 32 bit space
  - sbrk_bytes = (1 << IR::numBytesPerPageLog2) > UINT32_MAX ? UINT32_MAX : 1 << IR::numBytesPerPageLog2;
  + MemoryInstance* default_mem = Runtime::getDefaultMemory(code.instance);
  + sbrk_bytes = default_mem ? Runtime::getMemoryNumPages(default_mem) << IR::numBytesPerPageLog2 : 0;
  }
  wasm_cache::entry& code;
  apply_context& context;
  