Switch atmosphere's build target to C++20. (#952)

* ams: update to build with gcc10/c++20

* remove mno-outline-atomics

* ams: take care of most TODO C++20s

* fusee/sept: update for gcc10

* whoosh, your code now uses pre-compiled headers

* make: dependency fixes

libraries/libmesosphere/include/mesosphere/kern_k_auto_object.hpp

@@ -185,10 +185,7 @@ namespace ams::kern {
             T *obj;
         private:
             constexpr ALWAYS_INLINE void Swap(KScopedAutoObject &rhs) {
-                /* TODO: C++20 constexpr std::swap */
-                T *tmp = rhs.obj;
-                rhs.obj = this->obj;
-                this->obj = tmp;
+                std::swap(this->obj, rhs.obj);
             }
         public:
             constexpr ALWAYS_INLINE KScopedAutoObject() : obj(nullptr) { /* ... */ }