Add a testcase reduced from clang lto bootstrap on OS X.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222921 91177308-0d34-0410-b5e6-96231b3b80d8
Add an assert and use a range loop. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222922 91177308-0d34-0410-b5e6-96231b3b80d8