build: move source files from headers section

Currently, the sources list contains sources and headers which are
separated by a comment. I noticed two .cc files after the headers
comment and this commit moves those files the start of the list
where the rest of source files are.

PR-URL: https://github.com/nodejs/node/pull/10850


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>