Hopefully fixed the mingw32 build

src/thread/windows/SDL_systls.c

@@ -29,7 +29,12 @@
 #include "../SDL_thread_c.h"
 
 #if WINAPI_FAMILY_WINRT
+#include <fibersapi.h>
+
+#ifndef TLS_OUT_OF_INDEXES
 #define TLS_OUT_OF_INDEXES  FLS_OUT_OF_INDEXES
+#endif
+
 #define TlsAlloc()  FlsAlloc(NULL)
 #define TlsSetValue FlsSetValue
 #define TlsGetValue FlsGetValue