libstrat: enable -Wextra, -Werror

This caught an embarrassingly large number of bugs.

libraries/libstratosphere/source/fs/common/fs_file_storage.cpp

@@ -161,6 +161,8 @@ namespace ams::fs {
     }
 
     Result FileHandleStorage::OperateRange(void *dst, size_t dst_size, OperationId op_id, s64 offset, s64 size, const void *src, size_t src_size) {
+        AMS_UNUSED(src, src_size);
+
         switch (op_id) {
             case OperationId::QueryRange:
                 /* Validate buffer and size. */