cmGeneratorTarget: Drop default GetLinkerLanguage config argument

Update one remaining call site to avoid using the default.

Source/cmGeneratorTarget.h

@@ -534,7 +534,7 @@ public:
   std::string GetPDBDirectory(const std::string& config) const;
 
   ///! Return the preferred linker language for this target
-  std::string GetLinkerLanguage(const std::string& config = "") const;
+  std::string GetLinkerLanguage(const std::string& config) const;
 
   /** Does this target have a GNU implib to convert to MS format?  */
   bool HasImplibGNUtoMS() const;

Source/cmVisualStudio10TargetGenerator.cxx

@@ -1881,7 +1881,8 @@ bool cmVisualStudio10TargetGenerator::OutputSourceSpecificFlags(
   std::string lang =
     this->GlobalGenerator->GetLanguageFromExtension(sf.GetExtension().c_str());
   std::string sourceLang = this->LocalGenerator->GetSourceFileLanguage(sf);
-  const std::string& linkLanguage = this->GeneratorTarget->GetLinkerLanguage();
+  const std::string& linkLanguage =
+    this->GeneratorTarget->GetLinkerLanguage("");
   bool needForceLang = false;
   // source file does not match its extension language
   if (lang != sourceLang) {