compile with `-pthread` succeeded but the htmlpage no longer runs my code unless i remove `-pthread`

Please include the following in your bug report:

**Version of emscripten/emsdk:**
Please include the output `emcc -v` here
emcc 3.1.15

**Failing command line in full:**
If this is compile or link-time failure please include the full failing command
along with its entire output.

`
emcc main.c -std=c99 -o index.html -pthread -sPTHREAD_POOL_SIZE=navigator.hardwareConcurrency -lwebsocket.js -sASYNCIFY -sSINGLE_FILE -sFULL_ES3 -s USE_GLFW=3
`

if i remove
`-pthread -sPTHREAD_POOL_SIZE=navigator.hardwareConcurrency`

everything works as normal.

platform Windows