win32.h: fix for VC9

* include/ruby/win32.h (INTPTR_MAX, INTPTR_MIN, UINTPTR_MAX): split
  from intptr_t and uintptr_t, since VC9 defines the latters only in
  crtdefs.h.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40722 b2dd03c8-39d4-4d8f-98ff-823fe69b080e