regen/uconfig_h.pl can't be run (by default) by regen.pl, as regen.pl needs
to be cross-platform, whilst regen/uconfig_h.pl relies on having a Bourne
Shell. However, if one has managed to extract Makefile from Makefile.SH,
that's clear proof that one has a working Bourne Shell available :-)
regen: FORCE
-perl regen.pl
+ -perl regen/uconfig_h.pl
regen_headers: FORCE
-perl regen.pl -v
+ -perl regen/uconfig_h.pl -v
regen_meta: META.yml