cmGeneratorTarget: Drop obj libs from GetConfigCommonSourceFiles

Call sites such as those in the VS global generator that are used only
to reject per-config sources will now allow per-config object library
objects.  The corresponding generators have already been taught to deal
with per-config object library files.  Remaining call sites do not need
object library files anyway.

This will later allow `$<TARGET_OBJECTS:...>` generator expressions to
evaluate to values that vary by configuration (e.g. because each
configuration has its own object files).

Source/cmGeneratorTarget.cxx

@@ -949,6 +949,19 @@ void cmGeneratorTarget::GetSourceFiles(std::vector<cmSourceFile*>& files,
   }
 }
 
+void cmGeneratorTarget::GetSourceFilesWithoutObjectLibraries(
+  std::vector<cmSourceFile*>& files, const std::string& config) const
+{
+  KindedSources const& kinded = this->GetKindedSources(config);
+  files.reserve(kinded.Sources.size());
+  for (std::vector<SourceAndKind>::const_iterator si = kinded.Sources.begin();
+       si != kinded.Sources.end(); ++si) {
+    if (si->Source->GetObjectLibrary().empty()) {
+      files.push_back(si->Source);
+    }
+  }
+}
+
 cmGeneratorTarget::KindedSources const& cmGeneratorTarget::GetKindedSources(
   std::string const& config) const
 {
@@ -4937,11 +4950,11 @@ bool cmGeneratorTarget::GetConfigCommonSourceFiles(
 
   std::vector<std::string>::const_iterator it = configs.begin();
   const std::string& firstConfig = *it;
-  this->GetSourceFiles(files, firstConfig);
+  this->GetSourceFilesWithoutObjectLibraries(files, firstConfig);
 
   for (; it != configs.end(); ++it) {
     std::vector<cmSourceFile*> configFiles;
-    this->GetSourceFiles(configFiles, *it);
+    this->GetSourceFilesWithoutObjectLibraries(configFiles, *it);
     if (configFiles != files) {
       std::string firstConfigFiles;
       const char* sep = "";

Source/cmGeneratorTarget.h

@@ -70,6 +70,8 @@ public:
   bool GetPropertyAsBool(const std::string& prop) const;
   void GetSourceFiles(std::vector<cmSourceFile*>& files,
                       const std::string& config) const;
+  void GetSourceFilesWithoutObjectLibraries(std::vector<cmSourceFile*>& files,
+                                            const std::string& config) const;
 
   /** Source file kinds (classifications).
       Generators use this to decide how to treat a source file.  */
@@ -350,6 +352,9 @@ public:
   std::string GetFullNameImported(const std::string& config,
                                   bool implib) const;
 
+  /** Get source files common to all configurations and diagnose cases
+      with per-config sources.  Excludes sources added by a TARGET_OBJECTS
+      generator expression.  */
   bool GetConfigCommonSourceFiles(std::vector<cmSourceFile*>& files) const;
 
   bool HaveBuildTreeRPATH(const std::string& config) const;