VS: Only generate RC options if necessary

The RC options were computed and generated for every vcxproj file
before, even if no rc source was actually invocing the compiler.
Now we check first if we actually need to compute these.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -4001,9 +4001,12 @@ void cmVisualStudio10TargetGenerator::WriteClOptions(
 
 bool cmVisualStudio10TargetGenerator::ComputeRcOptions()
 {
-  return std::all_of(
-    this->Configurations.begin(), this->Configurations.end(),
-    [this](std::string const& c) { return this->ComputeRcOptions(c); });
+  return std::all_of(this->Configurations.begin(), this->Configurations.end(),
+                     [this](std::string const& c) {
+                       return !this->GeneratorTarget->IsLanguageUsed("RC",
+                                                                     c) ||
+                         this->ComputeRcOptions(c);
+                     });
 }
 
 bool cmVisualStudio10TargetGenerator::ComputeRcOptions(
@@ -4036,7 +4039,8 @@ bool cmVisualStudio10TargetGenerator::ComputeRcOptions(
 void cmVisualStudio10TargetGenerator::WriteRCOptions(
   Elem& e1, std::string const& configName)
 {
-  if (!this->MSTools) {
+  if (!this->MSTools ||
+      !this->GeneratorTarget->IsLanguageUsed("RC", configName)) {
     return;
   }
   Elem e2(e1, "ResourceCompile");