cmGlobalGenerator: factor out messaging for CMP0037

Also make some strings into character literals.

Source/cmGlobalGenerator.cxx

@@ -2690,13 +2690,9 @@ cmGlobalGenerator::SplitFrameworkPath(const std::string& path,
   return cm::nullopt;
 }
 
-bool cmGlobalGenerator::CheckCMP0037(std::string const& targetName,
-                                     std::string const& reason) const
+static bool RaiseCMP0037Message(cmake* cm, cmTarget* tgt,
+                                std::string const& reason)
 {
-  cmTarget* tgt = this->FindTarget(targetName);
-  if (!tgt) {
-    return true;
-  }
   MessageType messageType = MessageType::AUTHOR_WARNING;
   std::ostringstream e;
   bool issueMessage = false;
@@ -2715,13 +2711,12 @@ bool cmGlobalGenerator::CheckCMP0037(std::string const& targetName,
       break;
   }
   if (issueMessage) {
-    e << "The target name \"" << targetName << "\" is reserved " << reason
+    e << "The target name \"" << tgt->GetName() << "\" is reserved " << reason
       << ".";
     if (messageType == MessageType::AUTHOR_WARNING) {
       e << "  It may result in undefined behavior.";
     }
-    this->GetCMakeInstance()->IssueMessage(messageType, e.str(),
-                                           tgt->GetBacktrace());
+    cm->IssueMessage(messageType, e.str(), tgt->GetBacktrace());
     if (messageType == MessageType::FATAL_ERROR) {
       return false;
     }
@@ -2729,6 +2724,16 @@ bool cmGlobalGenerator::CheckCMP0037(std::string const& targetName,
   return true;
 }
 
+bool cmGlobalGenerator::CheckCMP0037(std::string const& targetName,
+                                     std::string const& reason) const
+{
+  cmTarget* tgt = this->FindTarget(targetName);
+  if (!tgt) {
+    return true;
+  }
+  return RaiseCMP0037Message(this->GetCMakeInstance(), tgt, reason);
+}
+
 void cmGlobalGenerator::CreateDefaultGlobalTargets(
   std::vector<GlobalTargetInfo>& targets)
 {