ams: mark ams::Result [[nodiscard]] (partially complete).

NOTE: This work is not yet fully complete; kernel is done, but
it was taking an exceedingly long time to get through libstratosphere.
Thus, I've temporarily added -Wno-error=unused-result for libstratosphere/stratosphere.

All warnings should be fixed to do the same thing Nintendo does as relevant, but this
is taking a phenomenally long time and is not actually the most important work to do,
so it can be put off for some time to prioritize other tasks for 21.0.0 support.

libraries/libmesosphere/include/mesosphere/kern_k_interrupt_event.hpp

@@ -38,13 +38,11 @@ namespace ams::kern {
 
             Result Reset();
 
-            Result Clear() {
+            void Clear() {
                 MESOSPHERE_ASSERT_THIS();
 
-                /* Try to perform a reset, succeeding unconditionally. */
-                this->Reset();
-
-                R_SUCCEED();
+                /* Try to perform a reset, ignoring whether it succeeds. */
+                static_cast<void>(this->Reset());
             }
 
             bool IsInitialized() const { return m_is_initialized; }