lr-mame needs significantly higher ram to build then free

[theofficialgman]

lr-mame compilation slows to a craw with only 4GB (ram+swap) allocated

as it is now, all ram+swap that retropie makes is filled during multiple parts of the lr-mame build, significantly slowing the build this is because of the variable number of threads that could be assigned for the build, when you spawn more threads for a build it is pretty much guaranteed that the ram usage will increase as some function of the number of threads used for compilation

maybe the rpSwap on function could be made to scale with the max_threads value?

rpSwap on 4096