Hi BPF and selftest maintainers.  I get a very strange failure
when trying to build the bpf selftests on current net-next master:

hch@brick:~/work/linux/tools/testing/selftests/bpf$ make
  GEN      vmlinux.h
Error: failed to load BTF from /home/hch/work/linux/vmlinux: No such file or directory
make: *** [Makefile:187: /home/hch/work/linux/tools/testing/selftests/bpf/tools/include/vmlinux.h]
Error 2
make: *** Deleting file '/home/hch/work/linux/tools/testing/selftests/bpf/tools/include/vmlinux.h'

But vmlinux obviously exists:

hch@brick:~/work/linux/tools/testing/selftests/bpf$ ls -l ~/work/linux/vmlinux
-rwxr-xr-x 1 hch hch 628909168 Jul 20 09:48 /home/hch/work/linux/vmlinux

.config attached.