had to switch from am3+ cpu to am3 cpu. ffmpeg "illegal instruction"

this is in 2 seperate funtoo linux installs, but gentoo is very close. i've been haveing constant crashes on my main box, and i've switched back to my previous. fx-4100 cpu back to adx640 athlon 2. i've spend a ton of time trying to find what libs or whatever have the newer fx-4100 instructions, and i'm failing. i've already rebuild world twice. i made a list of all installed apps with qlist, and rebuilt everything i could that still existed from that list. i custom emerged ffmpeg with -(everthing) that would still build, with the same results. i ran ldd ffmpeg, and everything in that list i checked and has been rebuilt. the 2 installs had cflags -march=native. luckily, my gentoo install had -mtune=native and no -march command. it's still fine. if i compile ffmpeg and mplayer by hand with configure and make, it works, so emerge is pulling in something with illegal instructions in it? that i can't find. how should i proceed?