I have followed the steps described in http://llvm.org/docs/Projects.html.
It seems there is a problem with the AutoRegen.sh script.
In order to get the whole sample project working in a directory
outside of llvm directory structure, I had to replace lines 22 and 23
I am not a configuration specialist, so I can't tell if this is a good
fix, but it works.
I should also add that in order to fully customize the sample project,
there is some additional work to rename existing directories and their
references in configure.ac. These additional steps are not described
in the "Creating an LLVM Project" document.