configure.in: setjmpex

* configure.in (setjmp-type): use setjmpex() on w64-mingw32 to get rid
  of -Wclobbered warnings.
* include/ruby/defines.h: include setjmpex.h here becase setjmp.h is
  included from win32.h via intrin.h, winnt.h, and so on.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40813 b2dd03c8-39d4-4d8f-98ff-823fe69b080e