Change how the linker handles the old llvm.global_ctors.

Change how the linker handles the old llvm.global_ctors.

Now instead of changing it to the new format and then linking, it just
handles the old format while copying it over.

The main differences are:

* There is no rauw in the source module.
* An old format input is always upgraded.

The first item helps with having a sane API that passes in a GV list to
the linker.

The second one is a small step in deprecating the old format.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254907 91177308-0d34-0410-b5e6-96231b3b80d8