[llvm-objcopy] Add --keep-file-symbols option

This option prevent from removing file symbols while removing symbols.

Differential Revision: https://reviews.llvm.org/D46830

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333339 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed