fix PR7742 / rdar://8250764, a miscompilation of struct

return where the struct has a base but no fields.  This
was because the x86-64 abi logic was checking the wrong
predicate in one place.

This was introduced in r91874, which was a fix for PR5831,
which lacked a CHECK line, so I verified and added it.

llvm-svn: 109759