scripts/pahole-flags.sh: Enable parallelization of pahole.

Pass a -j argument to pahole to parse DWARF and generate BTF with
multithreading (-j without arguments means one thread per CPU).
This also requires to check the version of pahole to then apply -j
only if >= v1.22.

Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220216193431.2691015-1-kuifeng@fb.com

scripts/pahole-flags.sh

@@ -16,5 +16,8 @@ fi
 if [ "${pahole_ver}" -ge "121" ]; then
 	extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
 fi
+if [ "${pahole_ver}" -ge "122" ]; then
+	extra_paholeopt="${extra_paholeopt} -j"
+fi
 
 echo ${extra_paholeopt}