Obviously, for admins only. Tested with admin, moderator, and not logged in.
Created attachment 75809 [details, diff] includes/page_header.php : adds code to create ACP link
Created attachment 75813 [details, diff] language/lang_english/lang_main.php : adds ACP reference Mainly did this so it was consistent with other code.
Created attachment 75843 [details, diff] language/lang_english/lang_extra.php : adds ACP reference
Created attachment 75844 [details, diff] templates/gentoo/overall_header.tpl : adds link to menu Used {ACP_LINK} method to more easily control appearance (or not) of ACP link and | characters.
Added, thanks pjp.