* enc/depend: fix inplace-build condition. enc.mk is generated with
setting $srcdir to enc, but pwd is still top build direcory.
[ruby-core:47236] [Bug #6888]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36725 b2dd03c8-39d4-4d8f-98ff-823fe69b080e