added import in order for alloca to work on macos (#1710)

src/external/stb_vorbis.h

@@ -570,7 +570,7 @@ enum STBVorbisError
    #if defined(_MSC_VER) || defined(__MINGW32__)
       #include <malloc.h>
    #endif
-   #if defined(__linux__) || defined(__linux) || defined(__EMSCRIPTEN__)
+   #if defined(__linux__) || defined(__linux) || defined(__EMSCRIPTEN__) || defined(__APPLE__)
       #include <alloca.h>
    #endif
 #else // STB_VORBIS_NO_CRT