sts: add STS_UNREACHABLE_DEFAULT_CASE()

stratosphere/libstratosphere/include/stratosphere/defines.hpp

@@ -21,6 +21,8 @@
 
 #define STS_ASSERT(expr) do { if (!(expr)) { std::abort(); } } while (0)
 
+#define STS_UNREACHABLE_DEFAULT_CASE() default: std::abort()
+
 #define NON_COPYABLE(cls) \
     cls(const cls&) = delete; \
     cls& operator=(const cls&) = delete