[llvm-objcopy][MachO] Add support for LC_CODE_SIGNATURE

This diff adds support for copying binaries
containing a LC_CODE_SIGNATURE load command.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D81768
diff --git a/llvm/tools/llvm-objcopy/MachO/Object.h b/llvm/tools/llvm-objcopy/MachO/Object.h
index b9ecd1e..5da31d2 100644
--- a/llvm/tools/llvm-objcopy/MachO/Object.h
+++ b/llvm/tools/llvm-objcopy/MachO/Object.h
@@ -302,9 +302,12 @@
   IndirectSymbolTable IndirectSymTable;
   LinkData DataInCode;
   LinkData FunctionStarts;
+  LinkData CodeSignature;
 
   Optional<uint32_t> SwiftVersion;
 
+  /// The index of LC_CODE_SIGNATURE load command if present.
+  Optional<size_t> CodeSignatureCommandIndex;
   /// The index of LC_SYMTAB load command if present.
   Optional<size_t> SymTabCommandIndex;
   /// The index of LC_DYLD_INFO or LC_DYLD_INFO_ONLY load command if present.