perf build: Make libunwind opt-in rather than opt-out

perf build: Make libunwind opt-in rather than opt-out

Having multiple unwinding libraries makes the perf code harder to
understand and we have unused/untested code paths.

Perf made BPF support an opt-out rather than opt-in feature. As libbpf
has a libelf dependency, elfutils that provides libelf will also
provide libdw. When libdw is present perf will use libdw unwinding
rather than libunwind unwinding even if libunwind support is compiled
in.

Rather than have libunwind built into perf and never used, explicitly
disable the support and make it opt-in.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20241028193619.247727-1-irogers@google.com
Closes: https://lore.kernel.org/linux-perf-users/CAP-5=fUXkp-d7gkzX4eF+nbjb2978dZsiHZ9abGHN=BN1qAcbg@mail.gmail.com/
Signed-off-by: Namhyung Kim <namhyung@kernel.org>