Missing buildlink3.mk for emacs added.
(1) Convert one SUBST_CLASS to REPLACE_PERL
(2) Add another SUBST_CLASS in the hope to solve following problem,
   /usr/pkg/bin/emacs -q -no-site-file -batch -l texinfmt -f batch-texinfo-format -I .;)
   >> /export/CHROOT/usr/pkgsrc/wip/tc-git/work/tc/doc/-I does not exist!
   But this problem doesn not always happen.