Apply most suggestions of clang-tidy's performance-unnecessary-value-param

Avoids unnecessary copies. All changes audited & pass tests with asan.
No functional change intended.

llvm-svn: 272190
diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index 14a2561..ff36f90 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -44,7 +44,7 @@
   /// The mover has just hit GV and we have to decide if it, and other members
   /// of the same comdat, should be linked. Every member to be linked is passed
   /// to Add.
-  void addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add);
+  void addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add);
 
   bool shouldLinkReferencedLinkOnce() {
     return !(Flags & Linker::DontForceLinkLinkonceODR);
@@ -416,7 +416,7 @@
   return false;
 }
 
-void ModuleLinker::addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add) {
+void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
   if (!shouldLinkReferencedLinkOnce())
     // For ThinLTO we don't import more than what was required.
     // The client has to guarantee that the linkonce will be availabe at link