I didn't try to compile it by myself, so I just did it. First time I ran it, it just crashed the same way (SIGBUS), but when I tried to run it within gdb it went just fine. Weird! Now it seems to work. I'm going to try the ebuild again to see what happens.
Thanks!
EDIT: I've tried the ebuild again and it worked! Since the last time I tried to emerge amule I didn't touch anything, I didn't reboot either....
EDIT2: I know what was the problem: I had no free space on the filesystem. KDE sometimes uses 3Gb or so of temp files, so I deleted the kde-temp folder. I didn't remember before.