Use do-while instead of a magic number. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@189413 91177308-0d34-0410-b5e6-96231b3b80d8
Modify test to adopt r189416.

r189416 changed the order of command line options shown in help message,
so the test needs adjusting.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@189417 91177308-0d34-0410-b5e6-96231b3b80d8