Completely disable signal handler on 32-bit (#1488)
Completely disable signal handler on 32-bit (#1488)

The previous change prevented `WASM_RT_MEMCHECK_SIGNAL_HANDLER_POSIX`
from being defined, but `WASM_RT_MEMCHECK_SIGNAL_HANDLER` was still
defined, which would prevent the memory bounds check.
WebAssembly/sexpr-wasm-prototype,WebAssembly/wabt,WebAssembly/wabt,WebAssembly/sexpr-wasm-prototype,WebAssembly/sexpr-wasm-prototype,WebAssembly/sexpr-wasm-prototype,WebAssembly/sexpr-wasm-prototype,WebAssembly/wabt,WebAssembly/sexpr-wasm-prototype,WebAssembly/wabt,WebAssembly/wabt