Created attachment 554512 [details]
Mednaffe only works with 1.21.1 or higher versions of mednafen emulator.
Update mednafen to 1.21.3:
The ebuild compiles and runs fine, but I still didn't took time to inspect src_prepare phase deeper to stick to the new release: see #comment 1 #641542
Bump mednaffe to 0.8.8 and check the required mednafen version.
Second way: revert mednaffe to 0.8.6