libbpf: Ignore warnings about "inefficient alignment"

Some consumers of libbpf compile the code base with different warnings
enabled. In a report for perf, for example, -Wpacked was set which
caused warnings about "inefficient alignment" to be emitted on a subset
of supported architectures.

With this change we silence specifically those warnings, as we intentionally
worked with packed structs.

This is a similar resolution as in b2f10cd4e805 ("perf cpumap: Fix alignment
for masks in event encoding").

Fixes: 1eebcb60633f ("libbpf: Implement basic zip archive parsing support")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/bpf/CA+G9fYtBnwxAWXi2+GyNByApxnf_DtP1-6+_zOKAdJKnJBexjg@mail.gmail.com/
Link: https://lore.kernel.org/bpf/20230315171550.1551603-1-deso@posteo.net

libbpf: Fix theoretical u32 underflow in find_cd() function

Coverity reported a potential underflow of the offset variable used in
the find_cd() function. Switch to using a signed 64 bit integer for the
representation of offset to make sure we can never underflow.

Fixes: 1eebcb60633f ("libbpf: Implement basic zip archive parsing support")
Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230307215504.837321-1-deso@posteo.net

libbpf: Implement basic zip archive parsing support

This change implements support for reading zip archives, including
opening an archive, finding an entry based on its path and name in it,
and closing it.
The code was copied from https://github.com/iovisor/bcc/pull/4440, which
implements similar functionality for bcc. The author confirmed that he
is fine with this usage and the corresponding relicensing. I adjusted it
to adhere to libbpf coding standards.

Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Michał Gregorczyk <michalgr@meta.com>
Link: https://lore.kernel.org/bpf/20230301212308.1839139-2-deso@posteo.net