Switch over to using SDL_GetTicks64()

SDL_GetTicks64() is a function that got added in SDL 2.0.18, which is
just an SDL_GetTicks() without a value that wraps every ~49 days,
instead wrapping after the sun explodes and kills us all. Oh sorry,
didn't mean to get existential.

For now, put this behind an SDL_VERSION_ATLEAST guard, which will be
removed when SDL 2.0.18 officially releases and we can update to it.

desktop_version/src/Script.cpp

@@ -3087,7 +3087,12 @@ void scriptclass::hardreset(void)
 {
     const bool version2_2 = GlitchrunnerMode_less_than_or_equal(Glitchrunner2_2);
 
+#if SDL_VERSION_ATLEAST(2, 0, 17)
+    /* The RNG is 32-bit. We don't _really_ need 64-bit... */
+    xoshiro_seed((Uint32) SDL_GetTicks64());
+#else
     xoshiro_seed(SDL_GetTicks());
+#endif
 
     //Game:
     game.hascontrol = true;