Object: constize Archive.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141448 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Object/Archive.cpp b/lib/Object/Archive.cpp
index 80343e3..aeb629b 100644
--- a/lib/Object/Archive.cpp
+++ b/lib/Object/Archive.cpp
@@ -156,14 +156,14 @@
   ec = object_error::success;
 }
 
-Archive::child_iterator Archive::begin_children() {
+Archive::child_iterator Archive::begin_children() const {
   const char *Loc = Data->getBufferStart() + Magic.size();
   size_t Size = sizeof(ArchiveMemberHeader) +
     ToHeader(Loc)->getSize();
   return Child(this, StringRef(Loc, Size));
 }
 
-Archive::child_iterator Archive::end_children() {
+Archive::child_iterator Archive::end_children() const {
   return Child(this, StringRef(0, 0));
 }