Created attachment 510652 [details]
There is a newer mednafen version. The sed lines in the ebuild needed some changes and I also made it use external libtremor and libmpcdec (as supported by the upstream build system). I also removed the -fstrict-aliasing cflag that was forced on by upstream.
Mednafen 1.22.1 got released on January 28, 2019 - 09:22 PST