PR17977: don't assume EOWNERDEAD is always defined

Summary: See details in http://llvm.org/bugs/show_bug.cgi?id=17977

Reviewers: dvyukov

Reviewed By: dvyukov

CC: glider, llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2340

llvm-svn: 196779