configure.in: setjmpex

* configure.in (setjmp-type): check if setjmpex() is really available.
  workaround for i686-w64-mingw32 which declares it but lacks its
  definition.
* include/ruby/defines.h: include setjmpex.h only if also setjmpex()
  is available.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40814 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-05-19

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40815 b2dd03c8-39d4-4d8f-98ff-823fe69b080e