perf bpf: Fix build with libbpf 0.7.0 by checking if bpf_program__set_insns() is available

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>

tools/perf/util/bpf-loader.c

@@ -36,6 +36,24 @@
 
 #include <internal/xyarray.h>
 
+#ifndef HAVE_LIBBPF_BPF_PROGRAM__SET_INSNS
+int bpf_program__set_insns(struct bpf_program *prog __maybe_unused,
+			   struct bpf_insn *new_insns __maybe_unused, size_t new_insn_cnt __maybe_unused)
+{
+	pr_err("%s: not support, update libbpf\n", __func__);
+	return -ENOTSUP;
+}
+
+int libbpf_register_prog_handler(const char *sec __maybe_unused,
+                                 enum bpf_prog_type prog_type __maybe_unused,
+                                 enum bpf_attach_type exp_attach_type __maybe_unused,
+                                 const struct libbpf_prog_handler_opts *opts __maybe_unused)
+{
+	pr_err("%s: not support, update libbpf\n", __func__);
+	return -ENOTSUP;
+}
+#endif
+
 /* temporarily disable libbpf deprecation warnings */
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"