win32.c: fix infinite recursion

* win32/win32.c: include "missing/nextafter.c" and address
  finite() and isnan() macros, to get rid of infinite recursion.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46004 b2dd03c8-39d4-4d8f-98ff-823fe69b080e