Merge branch 'selftests-bpf-Makefile-cleanup'

Andrii Nakryiko says:

====================
Patch #1 enforces libbpf build to have bpf_helper_defs.h ready before test BPF
programs are built.
Patch #2 drops obsolete BTF/pahole detection logic from Makefile.

v1->v2:
- drop CPU and PROBE (Martin).
====================

Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>