perf bpf: Avoid build breakage with libbpf < 0.8.0 + LIBBPF_DYNAMIC=1

In 746bd29e348f99b4 ("perf build: Use tools/lib headers from install
path") we stopped having the tools/lib/ directory from the kernel
sources in the header include path unconditionally, which breaks the
build on systems with older versions of libbpf-devel, in this case 0.7.0
as some of the structures and function declarations present in the newer
version of libbpf included in the kernel sources (tools/lib/bpf) are not
anymore used, just the ones in the system libbpf.

So instead of trying to provide alternative functions when the
libbpf-bpf_program__set_insns feature test fails, fail a
LIBBPF_DYNAMIC=1 build (requesting the use of the system's libbpf) and
emit this build error message:

$ make LIBBPF_DYNAMIC=1 -C tools/perf
Makefile.config:593: *** Error: libbpf devel library needs to be >= 0.8.0 to build with LIBBPF_DYNAMIC, update or build statically with the version that comes with the kernel sources. Stop.
$

For v6.3 these tests will be revamped and we'll require libbpf 1.0 as a
minimal version for using LIBBPF_DYNAMIC=1, most distros should have it
by now or at v6.3 time.

Fixes: 746bd29e348f99b4 ("perf build: Use tools/lib headers from install path")
Cc: Alexander Shishkin <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Mike Leach <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lore.kernel.org/lkml/CAP-5=[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Makefile.config

···
           $(call feature_check,libbpf-bpf_program__set_insns)
           ifeq ($(feature-libbpf-bpf_program__set_insns), 1)
             CFLAGS += -DHAVE_LIBBPF_BPF_PROGRAM__SET_INSNS
+          else
+            dummy := $(error Error: libbpf devel library needs to be >= 0.8.0 to build with LIBBPF_DYNAMIC, update or build statically with the version that comes with the kernel sources);
           endif
           $(call feature_check,libbpf-btf__raw_data)
           ifeq ($(feature-libbpf-btf__raw_data), 1)