Merge pull request #70 from waywardmonkeys/emscripten-def

Use __EMSCRIPTEN__ rather than EMSCRIPTEN.

include/bx/platform.h

@@ -175,7 +175,7 @@
 #elif defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
 #	undef  BX_PLATFORM_OSX
 #	define BX_PLATFORM_OSX 1
-#elif defined(EMSCRIPTEN)
+#elif defined(__EMSCRIPTEN__)
 #	undef  BX_PLATFORM_EMSCRIPTEN
 #	define BX_PLATFORM_EMSCRIPTEN 1
 #elif defined(__ORBIS__)