[llvm-strip] Support grouped options in llvm-strip

GNU and Apple `strip` implementations seems to support grouped options.
Enable the support for grouped options introduced in
https://reviews.llvm.org/D83639 for `llvm-strip` invocations.

Includes test that checks that both the grouped and non grouped
invocations produces the same result.

Reviewed By: alexander-shaposhnikov, MaskRay

Differential Revision: https://reviews.llvm.org/D105249