[CommandLine] Aliases require an value if their target requires a value.

This can still be overridden by explicitly setting a value requirement on the
alias option, but by default it should be the same.

PR18649

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200407 91177308-0d34-0410-b5e6-96231b3b80d8