Explicitly disable WASM_BIGINT in emcc build when the CMake flag is off (WebAssembly#7162)

This handles the case where WASM_BIGINT is enabled by default by emcc.
Binaryen's JS bindings do not currently work with bigint (see WebAssembly#7163)

Author: dschuff

CMakeLists.txt

@@ -337,6 +337,8 @@ if(EMSCRIPTEN)
   option(ENABLE_BIGINT "Enable wasm BigInt support" OFF)
   if(ENABLE_BIGINT)
     add_link_flag("-sWASM_BIGINT")
+   else()
+    add_link_flag("-sWASM_BIGINT=0")
   endif()
 
   if("${CMAKE_BUILD_TYPE}" MATCHES "Release")