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...

README Emscripten

Emscripten