common.mk: use PWD with nmake

* common.mk (ext/ripper/ripper.c): move MAKEDIR to Makefile.sub.

* win32/Makefile.sub (PWD): set to $(MAKEDIR), nmake built-in macro.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48531 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-11-22

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48532 b2dd03c8-39d4-4d8f-98ff-823fe69b080e