Similarly to bpftool Makefile, allow to specify custom location of vmlinux.h
to be used during the build. This allows simpler testing setups with
checked-in pre-generated vmlinux.h.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200630004759.521530-2-andriin@fb.com