There are many ways users may compile samples, some of them got
broken by commit 5f9380572b ("samples: bpf: compile and link
against full libbpf"). Improve path resolution and make libbpf
building a dependency of source files to force its build.
Samples should now again build with any of:
cd samples/bpf; make
make samples/bpf/
make -C samples/bpf
cd samples/bpf; make O=builddir
make samples/bpf/ O=builddir
make -C samples/bpf O=builddir
export KBUILD_OUTPUT=builddir
make samples/bpf/
make -C samples/bpf
Fixes: 5f9380572b ("samples: bpf: compile and link against full libbpf")
Reported-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
787360f8c2