Remove lto_codegen_set_attr.

It was never exported, so no functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214519 91177308-0d34-0410-b5e6-96231b3b80d8
[AArch64] Fix test from r214518 in an attempt to appease buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214521 91177308-0d34-0410-b5e6-96231b3b80d8