cmTarget: Make the source files depend on the config.

Disallow the use of config-specific source files with
the Visual Studio and Xcode generators. They don't have
any way to represent the condition currently.

Use the same common-config API in cmQtAutoGenerators. While
it accepts config-specific files, it doesn't have to support
multiple configurations yet.

Loop over the configs in cmTargetTraceDependencies
and cmGlobalGenerator::WriteSummary and consume all source
files.

Loop over the configs in cmComputeTargetDepends and compute the
object library dependencies for each config.

Source/cmNinjaNormalTargetGenerator.cxx

@@ -111,7 +111,8 @@ void cmNinjaNormalTargetGenerator::WriteLanguagesRules()
 #endif
 
   std::set<std::string> languages;
-  this->GetTarget()->GetLanguages(languages);
+  this->GetTarget()->GetLanguages(languages,
+                  this->GetMakefile()->GetSafeDefinition("CMAKE_BUILD_TYPE"));
   for(std::set<std::string>::const_iterator l = languages.begin();
       l != languages.end();
       ++l)