Fix the regular expression validator for target names.

Regression introduced by f1eacf0e07759b57d100dbf5d83c70e4028bcb54.
Target names have different valid contents to config names.

Source/cmGeneratorExpressionEvaluator.cxx

@@ -299,7 +299,7 @@ struct TargetFilesystemArtifact : public cmGeneratorExpressionNode
     std::string name = *parameters.begin();
 
     cmsys::RegularExpression targetValidator;
-    targetValidator.compile("^[A-Za-z0-9_]+$");
+    targetValidator.compile("^[A-Za-z0-9_.-]+$");
     if (!targetValidator.find(name.c_str()))
       {
       ::reportError(context, content->GetOriginalExpression(),