Initial merge of Emscripten port!

With this commit, you can compile SDL2 with Emscripten
( http://emscripten.org/ ), and make your SDL-based C/C++ program
into a web app.

This port was due to the efforts of several people, including: Charlie Birks,
Sathyanarayanan Gunasekaran, Jukka Jylänki, Alon Zakai, Edward Rudd,
Bruce Mitchener, and Martin Gerhardy. (Thanks, everyone!)

--HG--
extra : rebase_source : 97af74c8a5121e926ebe89f123536b5dd6681695

test/loopwave.c

@@ -24,6 +24,10 @@
 #include <signal.h>
 #endif
 
+#ifdef __EMSCRIPTEN__
+#include <emscripten/emscripten.h>
+#endif
+
 #include "SDL.h"
 #include "SDL_audio.h"
 
@@ -75,6 +79,13 @@ poked(int sig)
     done = 1;
 }
 
+void
+loop()
+{
+    if(done || (SDL_GetAudioStatus() != SDL_AUDIO_PLAYING))
+        emscripten_cancel_main_loop();
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -131,8 +142,13 @@ main(int argc, char *argv[])
 
     /* Let the audio run */
     SDL_PauseAudio(0);
+
+#ifdef __EMSCRIPTEN__
+    emscripten_set_main_loop(loop, 0, 1);
+#else
     while (!done && (SDL_GetAudioStatus() == SDL_AUDIO_PLAYING))
         SDL_Delay(1000);
+#endif
 
     /* Clean up on signal */
     SDL_CloseAudio();