linkage: the value may be replaced with something
different at link time. (Frontends that want to
allow values to be loaded out of weak constants can
give their constants weak_odr linkage).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67407 91177308-0d34-0410-b5e6-96231b3b80d8
