Fixed mingw64 32-bit build, which does have the correct structure definitions

src/audio/winmm/SDL_winmm.c

@@ -33,8 +33,8 @@
 #include "../SDL_audio_c.h"
 #include "SDL_winmm.h"
 
-/*====== WORKAROUND for MinGW's WinAPI header where those structures are being missed ======*/
-#if defined(__MINGW32__) && !defined(__MINGW64__)
+/* MinGW32 mmsystem.h doesn't include these structures */
+#if defined(__MINGW32__) && defined(_MMSYSTEM_H)
 
 typedef struct tagWAVEINCAPS2W 
 {
@@ -65,8 +65,7 @@ typedef struct tagWAVEOUTCAPS2W
     GUID NameGuid;
 } WAVEOUTCAPS2W,*PWAVEOUTCAPS2W,*NPWAVEOUTCAPS2W,*LPWAVEOUTCAPS2W;
 
-#endif /* defined(__MINGW32__) && !defined(__MINGW64__) */
-/*==========================================================================================*/
+#endif /* defined(__MINGW32__) && defined(_MMSYSTEM_H) */
 
 #ifndef WAVE_FORMAT_IEEE_FLOAT
 #define WAVE_FORMAT_IEEE_FLOAT 0x0003