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/libstratosphere/source/os/impl/os_resource_manager.cpp

@@ -18,7 +18,6 @@
 
 namespace ams::os::impl {
 
-    /* TODO: C++20 constinit */
-    TYPED_STORAGE(OsResourceManager) ResourceManagerHolder::s_resource_manager_storage = {};
+    constinit TYPED_STORAGE(OsResourceManager) ResourceManagerHolder::s_resource_manager_storage = {};
 
 }