[emscripten] Do not link to system libraries
[emscripten] Do not link to system libraries

This is not meaningful when compiling to javascript, and causes warning
at linking stage.

apavlenko/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv