[llvm-strip] Support --keep and --strip-all-gnu from llvm-objcopy

Summary: Add --keep and --strip-all-gnu from llvm-objcopy into llvm-strip.

Reviewers: jakehehrlich, jhenderson, alexshap

Reviewed By: jhenderson, alexshap

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53954

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345861 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed