general: Ignore implicit-fallthrough for SDL.h

SDL 2.0.14 introduces an incompatibility with Clang, causing it to
trigger -Wimplicit-fallthrough even though it is marked. Ignore it for
now, with a comment mentioning why this is needed.

src/yuzu_cmd/emu_window/emu_window_sdl2_gl.cpp

@@ -5,8 +5,18 @@
 #include <algorithm>
 #include <cstdlib>
 #include <string>
+
 #define SDL_MAIN_HANDLED
+// Ignore -Wimplicit-fallthrough due to https://github.com/libsdl-org/SDL/issues/4307
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wimplicit-fallthrough"
+#endif
 #include <SDL.h>
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 #include <fmt/format.h>
 #include <glad/glad.h>
 #include "common/assert.h"