Oh indeed. New Config piece starting from 5.12, this is why I didn't see it.
perlbrew exec perl -V:charbits
5.10.0_2
==========
charbits='UNKNOWN';
5.10.0_andk
==========
charbits='UNKNOWN';
5.10.0_dbg1
==========
charbits='UNKNOWN';
5.10.0_tr
==========
charbits='UNKNOWN';
5.10.1
==========
charbits='UNKNOWN';
5.10.1_2
==========
charbits='UNKNOWN';
5.10.1_dbg1
==========
charbits='UNKNOWN';
5.10.1_no_thr
==========
charbits='UNKNOWN';
5.12.0_dbg1
==========
charbits='8';
5.12.1
==========
charbits='8';
5.12.2
==========
charbits='8';
5.12.3
==========
charbits='8';
5.12.4
==========
charbits='8';
5.12.4_dbg1
==========
charbits='8';
5.12.5
==========
charbits='8';
5.12.5_nthr
==========
charbits='8';
5.14.1_thr
==========
charbits='8';
5.14.1_thr_mb_dbg
==========
charbits='8';
5.14.2_dbg_thr_mb
==========
charbits='8';
5.14.2_thr_cln
==========
charbits='8';
5.14.3
==========
charbits='8';
5.14.3_mad
==========
charbits='8';
5.14.3_nthr
==========
charbits='8';
5.15.8
==========
charbits='8';
5.15.9
==========
charbits='8';
5.16.0
==========
charbits='8';
5.16.2
==========
charbits='8';
5.16.2.1
==========
charbits='8';
5.16.2_mad
==========
charbits='8';
5.16.2_nthr
==========
charbits='8';
5.17.6
==========
charbits='8';
5.17.8
==========
charbits='8';
5.17.9
==========
charbits='8';
5.6.2
==========
charbits='UNKNOWN';
5.8.1
==========
charbits='UNKNOWN';
5.8.1_dbg_mb
==========
charbits='UNKNOWN';
5.8.2
==========
charbits='UNKNOWN';
5.8.3
==========
charbits='UNKNOWN';
5.8.3_cc
==========
charbits='UNKNOWN';
5.8.3_cln
==========
charbits='UNKNOWN';
5.8.3_cln2
==========
charbits='UNKNOWN';
5.8.3_dbg_thr
==========
charbits='UNKNOWN';
5.8.3_tr
==========
charbits='UNKNOWN';
5.8.4
==========
charbits='UNKNOWN';
5.8.4_cc
==========
charbits='UNKNOWN';
5.8.4_min
==========
charbits='UNKNOWN';
5.8.5
==========
charbits='UNKNOWN';
5.8.5_cc
==========
charbits='UNKNOWN';
5.8.5_clean_cattest
==========
charbits='UNKNOWN';
5.8.5_tr
==========
charbits='UNKNOWN';
5.8.6
==========
charbits='UNKNOWN';
5.8.7
==========
charbits='UNKNOWN';
5.8.7_cc
==========
charbits='UNKNOWN';
5.8.8
==========
charbits='UNKNOWN';
5.8.8_cpanmeta
==========
charbits='UNKNOWN';
5.8.8_dbg
==========
charbits='UNKNOWN';
5.8.9
==========
charbits='UNKNOWN';
5.8.9_dbg1
==========
charbits='UNKNOWN';
5.8.9_f
==========
charbits='UNKNOWN';
current
==========
charbits='UNKNOWN';
custom
==========
charbits='8';