Add noreturn qualifier to VVV_exit

This function doesn't return, so we mark it as noreturn if the compiler
supports it.

desktop_version/src/Exit.h

@@ -1,6 +1,14 @@
 #ifndef VVV_EXIT_H
 #define VVV_EXIT_H
 
-void VVV_exit(const int exit_code);
+#ifdef __GNUC__
+#   define VVV_NORETURN __attribute__((noreturn))
+#elif defined(_MSC_VER)
+#   define VVV_NORETURN __declspec(noreturn)
+#else
+#   define VVV_NORETURN
+#endif
+
+VVV_NORETURN void VVV_exit(const int exit_code);
 
 #endif /* VVV_EXIT_H */