I started building LFS the other day. I was very careful to not skip instructions, but because the build was fairly discontinuous (spread over a week or so) I suppose I could have missed a step. Somewhere about halfway through chapter 6, I got an error that an include was missing. It was than that I noticed I had built in two targets within my $LFS/tools directory: x86_64-lfs-linux-gnu, and x86_64-unknown-linux-gnu. I had backed up my tool chain at the end of chapter 5 so I double checked to see if I had two targets at that point. I did. Finally, I decided to just start all over. I was very careful to check $LFS_TGT variable regularly. Before step 5.11, right after gcc pass 2 I double checked the /tools directory. Same thing again. My target variable was still set. I have been copy and pasting all expressions to avoid mistyping. The lfs target has an include directory while the unknown does not. They both appear to have binutils binaries.

I can't figure out what I would have done. Any ideas?

Is it possible that the error occurred somewhere prior to chapter 5?? I'm wondering if that is when it occurred since you said that the backup of the tool chain at the end of chapter 5 already had two target points. Some of the errors I received when building my first LFS (last week lol) were able to be solved via going back to the first chapter and sort of re-tracing my steps. I reviewed the steps and thought "oh yeah... i did do that..or sometimes it was oh wait, I did that wrong" and it helped out.

That's what it needs to be. x86_64-lfs-linux-gnu-gcc is treated as a cross-compiler on auto-detected x86_64-unknown-linux-gnu host.

A cross compiler is needed to compile a toolchain that isn't dependent on the host toolchain, aka x86_64-unknown-linux-gnu-gcc.