* common.mk: enc/unicode.$(OBJEXT) depends on onigmo.h via
oniguruma.h.
* common.mk: dependencies of *prelude.$(OBJEXT) are defined for
each generated C sources.
* enc/depend: casefold.h and name2ctype.h are located under
$(UNICODE_HDR_DIR).
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61800 b2dd03c8-39d4-4d8f-98ff-823fe69b080e