Improve wasm debug build (#4842)
Improve wasm debug build (#4842)

When building Binaryen to wasm in debug mode,
1) Avoid post-link Binaryen changes with WASM_BIGINT and by avoiding O3
2) Don't use SINGLE_FILE, to make it easier to analyze the resulting wasm
WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen