"/bin/sh: line 1: 10086 Illegal instruction"
see that it occurs at your message
When I emerge xorg-x11 , and the system also give same error message "Illegal instruction" ...but now I overcome the problem.
I just think you maybe install gentoo form stage-3 ...
so .. Maybe you choose wrong version stage-3 ...
Wrong version stage just means "It can't fit your Processor"!
So when you emerge some software will occur ERROR message shch that "Illegal instruction"
So maybe you can choose x86 or i686 stage3 if your computer system is x86 ...