Until sr#822399 we accidentally had assertions enabled in 32-bit architectures, and i586 is the only 32-bit arch where we build the aarch64 backend. (On armv{6,7}l we don't build it, for example.)

That's why you see the assertion failure only there.

Now you have two choices:

• port that change back and ignore the assertion failure, which could indicate a problem though, or
• try to figure out what's going wrong. Looking at the log between 9 (where we have the same error) and 10, it could be D67189 or D68711, but most likely D66337. If you can't find anything, try asking in #llvm on irc.oftc.net.