dmyenc.c: separate

* dmyenc.c (Init_enc): separate from dmyext.c for statically
  linked extension excluding encoding libraries.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48623 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
common.mk: INITOBJS

* common.mk (INITOBJS): rename DMYEXT.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48624 b2dd03c8-39d4-4d8f-98ff-823fe69b080e