Merge branch 'runqslower'

Andrii Nakryiko says:

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Based on recent BPF CO-RE, tp_btf, and BPF skeleton changes, re-implement
BCC-based runqslower tool as a portable pre-compiled BPF CO-RE-based tool.
Make sure it's built as part of selftests to ensure it doesn't bit rot.

As part of this patch set, augment `format c` output of `bpftool btf dump`
sub-command with applying `preserve_access_index` attribute to all structs and
unions. This makes all such structs and unions automatically relocatable under
BPF CO-RE, which improves user experience of writing TRACING programs with
direct kernel memory read access.

Also, further clean up selftest/bpf Makefile output and make it conforming to
libbpf and bpftool succinct output format.

v1->v2:
- build in-tree bpftool for runqslower (Yonghong);
- drop `format core` and augment `format c` instead (Alexei);
- move runqslower under tools/bpf (Daniel).
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Signed-off-by: Alexei Starovoitov <ast@kernel.org>