libstrat: enable -Wextra, -Werror

This caught an embarrassingly large number of bugs.

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

@@ -257,7 +257,7 @@ namespace ams::lmem::impl {
         AMS_ASSERT(static_cast<s32>(MinimumAlignment) <= alignment);
         AMS_ASSERT(unit_size >= sizeof(uintptr_t));
 
-        return (alignment - 1) + util::AlignUp(unit_size, alignment) + (internal_metadata ? sizeof(HeapHead) : 0);
+        return (alignment - 1) + (unit_count * util::AlignUp(unit_size, alignment)) + (internal_metadata ? sizeof(HeapHead) : 0);
     }
 
 }