Use one authorative source of the LINK_LIBRARIES property.

We populate and maintain a vector of structs to keep track of
backtraces already, so no need to populate the Properties container
additionally.

For completeness, it is necessary to remove the condition for
populating the vector for only valid library names and generator
expressions. That condition is now determined when evaluating the
generator expressions.

Source/cmTarget.cxx

@@ -2657,6 +2657,11 @@ void cmTarget::FinalizeSystemIncludeDirectories()
       end = this->Internal->LinkInterfacePropertyEntries.end();
       it != end; ++it)
     {
+    if (!cmGeneratorExpression::IsValidTargetName(it->Value)
+        && cmGeneratorExpression::Find(it->Value) == std::string::npos)
+      {
+      continue;
+      }
     {
     cmListFileBacktrace lfbt;
     cmGeneratorExpression ge(lfbt);
@@ -3033,15 +3038,11 @@ void cmTarget::SetProperty(const char* prop, const char* value)
   if (strcmp(prop, "LINK_LIBRARIES") == 0)
     {
     this->Internal->LinkInterfacePropertyEntries.clear();
-    if (cmGeneratorExpression::IsValidTargetName(value)
-        || cmGeneratorExpression::Find(value) != std::string::npos)
-      {
     cmListFileBacktrace lfbt;
     this->Makefile->GetBacktrace(lfbt);
     cmValueWithOrigin entry(value, lfbt);
     this->Internal->LinkInterfacePropertyEntries.push_back(entry);
-      }
+    return;
-    // Fall through
     }
   this->Properties.SetProperty(prop, value, cmProperty::TARGET);
   this->MaybeInvalidatePropertyCache(prop);
@@ -3099,15 +3100,11 @@ void cmTarget::AppendProperty(const char* prop, const char* value,
     }
   if (strcmp(prop, "LINK_LIBRARIES") == 0)
     {
-    if (cmGeneratorExpression::IsValidTargetName(value)
-        || cmGeneratorExpression::Find(value) != std::string::npos)
-      {
     cmListFileBacktrace lfbt;
     this->Makefile->GetBacktrace(lfbt);
     cmValueWithOrigin entry(value, lfbt);
     this->Internal->LinkInterfacePropertyEntries.push_back(entry);
-      }
+    return;
-    // Fall through
     }
   this->Properties.AppendProperty(prop, value, cmProperty::TARGET, asString);
   this->MaybeInvalidatePropertyCache(prop);
@@ -3387,6 +3384,11 @@ std::vector<std::string> cmTarget::GetIncludeDirectories(const char *config)
         end = this->Internal->LinkInterfacePropertyEntries.end();
         it != end; ++it)
       {
+      if (!cmGeneratorExpression::IsValidTargetName(it->Value)
+          && cmGeneratorExpression::Find(it->Value) == std::string::npos)
+        {
+        continue;
+        }
       {
       cmGeneratorExpression ge(lfbt);
       cmsys::auto_ptr<cmCompiledGeneratorExpression> cge =
@@ -3585,6 +3587,11 @@ void cmTarget::GetCompileOptions(std::vector<std::string> &result,
         end = this->Internal->LinkInterfacePropertyEntries.end();
         it != end; ++it)
       {
+      if (!cmGeneratorExpression::IsValidTargetName(it->Value)
+          && cmGeneratorExpression::Find(it->Value) == std::string::npos)
+        {
+        continue;
+        }
       {
       cmGeneratorExpression ge(lfbt);
       cmsys::auto_ptr<cmCompiledGeneratorExpression> cge =
@@ -3693,6 +3700,11 @@ void cmTarget::GetCompileDefinitions(std::vector<std::string> &list,
         end = this->Internal->LinkInterfacePropertyEntries.end();
         it != end; ++it)
       {
+      if (!cmGeneratorExpression::IsValidTargetName(it->Value)
+          && cmGeneratorExpression::Find(it->Value) == std::string::npos)
+        {
+        continue;
+        }
       {
       cmGeneratorExpression ge(lfbt);
       cmsys::auto_ptr<cmCompiledGeneratorExpression> cge =
@@ -4181,6 +4193,22 @@ const char *cmTarget::GetProperty(const char* prop,
       }
     return output.c_str();
     }
+  if(strcmp(prop,"LINK_LIBRARIES") == 0)
+    {
+    static std::string output;
+    output = "";
+    std::string sep;
+    for (std::vector<cmValueWithOrigin>::const_iterator
+        it = this->Internal->LinkInterfacePropertyEntries.begin(),
+        end = this->Internal->LinkInterfacePropertyEntries.end();
+        it != end; ++it)
+      {
+      output += sep;
+      output += it->Value;
+      sep = ";";
+      }
+    return output.c_str();
+    }
 
   if (strcmp(prop,"IMPORTED") == 0)
     {