To allow the build to complete on older systems, where those files are
either not uptodate, lacking some recent additions or not present at
all.
And check if the copy drifts from the kernel, as in this synthetic test:
BUILD: Doing 'make -j4' parallel build
Warning: tools/include/linux/bpf.h differs from kernel
Warning: tools/include/linux/bpf_common.h differs from kernel
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-5plvi2gq4x469dcyybiu226q@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
