Dropping old debug format requires the entire module to be read upfront.
This was failing only with the gold plugin, but that is just because
llvm-link was not upgrading metadata.
The new testcase using llvm-link shows the problem.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233381 91177308-0d34-0410-b5e6-96231b3b80d8
