[NFC][llvm-objcopy] Cleanup namespace usage in llvm-objcopy.

Nest any classes not used outside of a file into anon. Nest any classes used
across files in llvm-objcopy into namespace llvm::objcopy.


Differential Revision: https://reviews.llvm.org/D49449





git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337337 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed