[ORC] Rename SearchOrder operations on JITDylib to LinkOrder.

Refering to the link order of a dylib better matches the terminology used in
static compilation. As upcoming patches will increase the number of places where
link order matters (for example when closing JITDylibs) it's better to get this
name change out of the way early.
diff --git a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
index 9058a79..961cd77 100644
--- a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
+++ b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
@@ -657,13 +657,13 @@
     // Set every dylib to link against every other, in command line order.
     for (auto *JD : S.JDSearchOrder) {
       auto LookupFlags = JITDylibLookupFlags::MatchExportedSymbolsOnly;
-      JITDylibSearchOrder O;
+      JITDylibSearchOrder LinkOrder;
       for (auto *JD2 : S.JDSearchOrder) {
         if (JD2 == JD)
           continue;
-        O.push_back(std::make_pair(JD2, LookupFlags));
+        LinkOrder.push_back(std::make_pair(JD2, LookupFlags));
       }
-      JD->setSearchOrder(std::move(O));
+      JD->setLinkOrder(std::move(LinkOrder));
     }
   }