win32.h: INTPTR_MAX, INTPTR_MIN, UINTPTR_MAX

* include/ruby/win32.h (INTPTR_MAX, INTPTR_MIN, UINTPTR_MAX): also
  should be defined when defining intptr_t and uintptr_t.
  bigdecimal.c requires the former two now.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40567 b2dd03c8-39d4-4d8f-98ff-823fe69b080e