Use SDL_FALLTHROUGH if available

The SDL_FALLTHROUGH macro has been added to SDL 2.0.18. Until 2.0.18 is
released, use it if it's available.

desktop_version/src/Graphics.cpp

@@ -12,6 +12,7 @@
 #include "Map.h"
 #include "Music.h"
 #include "Screen.h"
+#include "TempSDLFallthrough.h"
 #include "UtilityClass.h"
 #include "Vlogging.h"
 
@@ -591,7 +592,7 @@ bool Graphics::next_wrap(
             break;
         case '\n':
             *start += 1;
-            VVV_fallthrough;
+            SDL_FALLTHROUGH;
         case '\0':
             return true;
         }

desktop_version/src/TempSDLFallthrough.h

@@ -0,0 +1,22 @@
+#ifndef TEMPSDLFALLTHROUGH_H
+#define TEMPSDLFALLTHROUGH_H
+
+/* FIXME: Delete this when SDL 2.0.18 releases! */
+
+#include <SDL_stdinc.h>
+
+#ifndef SDL_FALLTHROUGH
+#   ifndef __has_attribute
+#      define __has_attribute(x) 0
+#   endif
+
+#   if __has_attribute(__fallthrough__)
+#      define VVV_fallthrough __attribute__((__fallthrough__))
+#   else
+#      define VVV_fallthrough do { } while (false) /* fallthrough */
+#   endif
+
+#   define SDL_FALLTHROUGH VVV_fallthrough
+#endif
+
+#endif /* TEMPSDLFALLTHROUGH_H */

desktop_version/src/UtilityClass.h

@@ -68,16 +68,6 @@ void _VVV_between(
         sizeof(middle) \
     )
 
-#ifndef __has_attribute
-#   define __has_attribute(x) 0
-#endif
-
-#if __has_attribute(__fallthrough__)
-#   define VVV_fallthrough __attribute__((__fallthrough__))
-#else
-#   define VVV_fallthrough do { } while (false) /* fallthrough */
-#endif
-
 #define MAYBE_FAIL(expr) \
     do \
     { \