[PCH] Remove building a SmallPtrSet that is not actually used for anything.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176354 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Serialization/ASTWriter.cpp

@@ -1758,12 +1758,10 @@ void ASTWriter::WritePreprocessor(const Preprocessor &PP, bool IsModule) {
   // Construct the list of macro definitions that need to be serialized.
   SmallVector<std::pair<const IdentifierInfo *, MacroDirective *>, 2>
     MacrosToEmit;
-  llvm::SmallPtrSet<const IdentifierInfo*, 4> MacroDefinitionsSeen;
   for (Preprocessor::macro_iterator I = PP.macro_begin(Chain == 0),
                                     E = PP.macro_end(Chain == 0);
        I != E; ++I) {
     if (!IsModule || I->second->isPublic()) {
-      MacroDefinitionsSeen.insert(I->first);
       MacrosToEmit.push_back(std::make_pair(I->first, I->second));
     }
   }