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/source/kern_k_object_name.cpp

@@ -19,9 +19,8 @@ namespace ams::kern {
 
     namespace {
 
-        /* TODO: C++20 constinit */
-        KLightLock g_object_list_lock;
-        KObjectName::List g_object_list;
+        constinit KLightLock g_object_list_lock;
+        constinit KObjectName::List g_object_list;
 
     }