[lib/LTO] Don't reinvent the code for switching linkage

[pcc]

LGTM

llvm/trunk/lib/LTO/LTO.cpp

for (const InputFile::Symbol &Sym : Syms) {
     ModuleSymbolTable::Symbol Msym = *MsymI++;
     Skip();
 
     if (GlobalValue *GV = Msym.dyn_cast<GlobalValue *>()) {
       if (Res.Prevailing) {
         if (Sym.isUndefined())
           continue;
         Keep.push_back(GV);
-        switch (GV->getLinkage()) {
-        default:
-          break;
-        case GlobalValue::LinkOnceAnyLinkage:
-          GV->setLinkage(GlobalValue::WeakAnyLinkage);
-          break;
-        case GlobalValue::LinkOnceODRLinkage:
-          GV->setLinkage(GlobalValue::WeakODRLinkage);
-          break;
-        }
+        GlobalValue::LinkageTypes OriginalLinkage = GV->getLinkage();
+        if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
+          GV->setLinkage(GlobalValue::getWeakLinkage(
+              GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
       } else if (isa<GlobalObject>(GV) &&
                  (GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage() ||
                   GV->hasAvailableExternallyLinkage()) &&
                  !AliasedGlobals.count(cast<GlobalObject>(GV))) {
         // Either of the above three types of linkage indicates that the
         // chosen prevailing symbol will have the same semantics as this copy of
         // the symbol, so we can link it with available_externally linkage. We
         // only need to do this if the symbol is undefined.