Add initial support for fast-isel of the [SU]ADDO intrinsics. It isn't

complete. For instance, it lowers the common case into this less-than-optimal
code:

        addl    %ecx, %eax
        seto    %cl
        testb   %cl, %cl
        jne     LBB1_2  ## overflow

instead of:

        addl    %ecx, %eax
        jo      LBB1_2  ## overflow

That will come in a future commit.

llvm-svn: 60737