During the transition to libbpf 1.0 some functions that perf used were
deprecated and finally removed from libbpf, so bpf_program__set_insns()
was introduced for perf to continue to use its bpf loader.

But when build with LIBBPF_DYNAMIC=1 we now need to check if that
function is available so that perf can build with older libbpf versions,
even if the end result is emitting a warning to the user that the use
of the perf BPF loader requires a newer libbpf, since bpf_program__set_insns()
touches libbpf objects internal state.

This affects only 'perf trace' when using bpf C code or pre-compiled
bytecode as an event.

Noticed on RHEL9, that has libbpf 0.7.0, where bpf_program__set_insns()
isn't available.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>