WIP: Build wasm emscripten

This branch will suggest patches for the following libvlc configuration :

emconfigure ../configure --build=x86_64-pc-linux-gnu --host=wasm32-local-emscripten --enable-debug --enable-gles2 --enable-merge-ffmpeg --disable-lua --disable-dca --disable-jpeg --disable-libmpeg2 --disable-aribb25 --disable-nls --disable-sout --disable-vlm --disable-addonmanagermodules --enable-avcodec --disable-swscale --disable-a52 --disable-x264 --disable-macosx --disable-sparkle --disable-qt --disable-screen --disable-xcb --disable-pulse --disable-alsa --disable-oss -disable-vlc --disable-ssp ac_cv_func_sendmsg=yes ac_cv_func_recvmsg=yes ac_cv_func_if_nameindex=yes ac_cv_header_search_h=no ac_cv_header_time_h=no ac_cv_header_sys_shm_h=no --disable-projectm --disable-vsxu