Fix use-after-free bug identified by the Address Sanitizer
Fix use-after-free bug identified by the Address Sanitizer

atomContent's memory is freed at the end of the stack frame,
but it is referenced by the atom pushed into _definedAtoms.

Differential Revision: http://reviews.llvm.org/D7732

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@229749 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld