libstrat: enable -Wextra, -Werror

This caught an embarrassingly large number of bugs.

libraries/libstratosphere/source/lmem/impl/lmem_impl_common_heap.cpp

@@ -45,6 +45,7 @@ namespace ams::lmem::impl {
 
     void FinalizeHeap(HeapHead *heap) {
         /* Nothing actually needs to be done here. */
+        AMS_UNUSED(heap);
     }
 
     bool ContainsAddress(HeapHandle handle, const void *address) {