ref: 2dda16bd69c4b17834d29b4e3f75d9bd973a81df
dir: /external/SDL2/docs/README-emscripten.md/
Emscripten
================================================================================
Build:
    $ mkdir build
    $ cd build
    $ emconfigure ../configure --host=asmjs-unknown-emscripten --disable-assembly --disable-threads --disable-cpuinfo CFLAGS="-O2"
    $ emmake make
Or with cmake:
    $ mkdir build
    $ cd build
    $ emcmake cmake ..
    $ emmake make
To build one of the tests:
    $ cd test/
    $ emcc -O2 --js-opts 0 -g4 testdraw2.c -I../include ../build/.libs/libSDL2.a ../build/libSDL2_test.a -o a.html
Uses GLES2 renderer or software
Some other SDL2 libraries can be easily built (assuming SDL2 is installed somewhere):
SDL_mixer (http://www.libsdl.org/projects/SDL_mixer/):
    $ EMCONFIGURE_JS=1 emconfigure ../configure
    build as usual...
SDL_gfx (http://cms.ferzkopp.net/index.php/software/13-sdl-gfx):
    $ EMCONFIGURE_JS=1 emconfigure ../configure --disable-mmx
    build as usual...