Update backend notes for Emscripten.

Emscripten no longer supports the -std=c* and -ansi compiler flags.

examples/build/ma_build_examples_emscripten.bat

-emcc ../simple_playback_emscripten.c -o ../bin/simple_playback_emscripten.html -s WASM=0 -std=c89 -ansi -Wall
\ No newline at end of file
+emcc ../simple_playback_emscripten.c -o ../bin/simple_playback_emscripten.html -s WASM=0 -Wall
\ No newline at end of file

miniaudio.h

@@ -320,6 +320,7 @@ UWP
 
 Web Audio / Emscripten
 ----------------------
+- You cannot use -std=c* compiler flags, nor -ansi. This only applies to the Emscripten build.
 - The first time a context is initialized it will create a global object called "miniaudio" whose primary purpose is to act
   as a factory for device objects.
 - Currently the Web Audio backend uses ScriptProcessorNode's, but this may need to change later as they've been deprecated.