Linker: Fix ASan failure from r243961

r243883 and r243961 made a use-after-free far more likely:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/6041/steps/check-llvm%20asan/logs/stdio

Unresolved nodes get inserted into the `Cycles` array.  If they later
get resolved through RAUW, we need to update the reference.  It's
interesting that this never hit before (maybe an asan-ified clang
bootstrap with `-flto -g` would have hit it, but I admit I haven't tried
anything quite that crazy).

llvm-svn: 243976