[dsymutil] Print warning/error for unknown/missing arguments.

After changing dsymutil to use libOption, we lost error reporting for
missing required arguments (input files). Additionally, we stopped
complaining about unknown arguments. This patch fixes both and adds a
test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375044 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed