[llvm-objcopy] Refactor ELF-specific config out to ELFCopyConfig. NFC.

Summary:
This patch splits the command-line parsing into two phases:

First, parse cross-platform options and leave ELF-specific options unparsed.

Second, in the ELF implementation, parse ELF-specific options and construct ELFCopyConfig.

Reviewers: espindola, alexshap, rupprecht, jhenderson, jakehehrlich, MaskRay

Reviewed By: alexshap, jhenderson, jakehehrlich, MaskRay

Subscribers: mgorny, emaste, arichardson, jakehehrlich, MaskRay, abrachet, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67139

llvm-svn: 372712
diff --git a/llvm/tools/llvm-objcopy/CMakeLists.txt b/llvm/tools/llvm-objcopy/CMakeLists.txt
index d281bf8..50c890b 100644
--- a/llvm/tools/llvm-objcopy/CMakeLists.txt
+++ b/llvm/tools/llvm-objcopy/CMakeLists.txt
@@ -21,6 +21,7 @@
   COFF/Object.cpp
   COFF/Reader.cpp
   COFF/Writer.cpp
+  ELF/ELFConfig.cpp
   ELF/ELFObjcopy.cpp
   ELF/Object.cpp
   MachO/MachOObjcopy.cpp