In this diff we move out the hierarchy of buffers from Object.h/Object.cpp
into separate files since it is not ELF-specific and will be reused later.
After this change Object.h/Object.cpp are almost exclusively ELF-specific.
Test plan: make check-all
Differential revision: https://reviews.llvm.org/D53298
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344585 91177308-0d34-0410-b5e6-96231b3b80d8
