Merge branch 'ease-bpf-signing-build-requirements'

Alan Maguire says:

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Ease BPF signing build requirements

This series makes it easier to build bpftool and selftests with
signing support, removing reliance on >= openssl v3 (supporting
openssl v1) to build bpftool and not requiring latest xxd to
build verification cert header in selftests.

Changes since v1 [1]:

- Updated patch 2 to add symlink test_progs_verification_cert to .gitignore,
  EXTRA_CLEANFILES (AI review bot)
- Added acks to patch 1 (Song, Quentin)

[1] https://lore.kernel.org/bpf/20251114222249.30122-1-alan.maguire@oracle.com/
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Link: https://patch.msgid.link/20251120084754.640405-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>