clang-tidy: fix `performance-unnecessary-copy-initialization` lints

Source/cmGlobalVisualStudio7Generator.cxx

@@ -426,7 +426,7 @@ void cmGlobalVisualStudio7Generator::WriteTargetsToSolution(
     cmValue expath = target->GetProperty("EXTERNAL_MSPROJECT");
     if (expath) {
       std::string project = target->GetName();
-      std::string location = *expath;
+      std::string const& location = *expath;
 
       this->WriteExternalProject(fout, project, location,
                                  target->GetProperty("VS_PROJECT_TYPE"),
@@ -506,7 +506,7 @@ void cmGlobalVisualStudio7Generator::WriteFoldersContent(std::ostream& fout)
     std::string guidParent(this->GetGUID(key));
 
     for (std::string const& it : iter.second) {
-      std::string value(it);
+      std::string const& value(it);
       std::string guid(this->GetGUID(value));
 
       fout << "\t\t{" << guid << "} = {" << guidParent << "}\n";

Source/cmVisualStudio10TargetGenerator.cxx

@@ -424,7 +424,7 @@ void cmVisualStudio10TargetGenerator::Generate()
     cmStrCat(this->LocalGenerator->GetCurrentBinaryDirectory(), '/',
              this->Name, ProjectFileExtension);
   cmGeneratedFileStream BuildFileStream(path);
-  const std::string PathToProjectFile = path;
+  const std::string& PathToProjectFile = path;
   BuildFileStream.SetCopyIfDifferent(true);
 
   // Write the encoding header into the file