Sys::Mmap is a perl module that has no ebuild. During Zoneminder install I installed Sys::Mmap through g-cpan. It worked without problems. I'm requesting that an ebuild for Sys::Mmap is created so Zoneminder can have it's own ebuild also. The default g-cpan generated ebuild works just fine, AFAICT.
added to the main tree as dev-perl/Sys-Mmap-0.160.0