Fix access to undefined weak symbols in pic code

When the access to a weak symbol is not a call, the access has to be
able to produce the value 0 at runtime.

We were sometimes producing code sequences where that was not possible
if the code was leaded more than 4g away from 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310756 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed