The linker will call `lto_codegen_add_must_preserve_symbol' on all globals that
should be kept around. The linker will pretend that a dylib is being created.
<rdar://problem/12528059>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169770 91177308-0d34-0410-b5e6-96231b3b80d8