[llvm-objcopy][MachO] Print an error message on use of unsupported options

[llvm-objcopy][MachO] Print an error message on use of unsupported options

Summary:
It is better to print an error message instead of silently ignoring unsupported options.

As mentioned in https://reviews.llvm.org/D57045, this is not the best solution and we should print which flag is not supported at some time.

Reviewers: alexshap, rupprecht, jhenderson, jakehehrlich

Reviewed By: alexshap, rupprecht, jakehehrlich

Subscribers: jakehehrlich, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62578

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362040 91177308-0d34-0410-b5e6-96231b3b80d8