Xcode: Sort source files

Since Xcode doesn't sort the files on its own, let's sort them in our
generator to make navigation easier.  Visual Studio, QtCreator, and
kdevelop all display files sorted.

Source/cmGlobalXCodeGenerator.cxx

@@ -955,6 +955,15 @@ void cmGlobalXCodeGenerator::SetCurrentLocalGenerator(cmLocalGenerator* gen)
     }
 }
 
+//----------------------------------------------------------------------------
+struct cmSourceFilePathCompare
+{
+  bool operator()(cmSourceFile* l, cmSourceFile* r)
+  {
+    return l->GetFullPath() < r->GetFullPath();
+  }
+};
+
 //----------------------------------------------------------------------------
 void
 cmGlobalXCodeGenerator::CreateXCodeTargets(cmLocalGenerator* gen,
@@ -981,7 +990,9 @@ cmGlobalXCodeGenerator::CreateXCodeTargets(cmLocalGenerator* gen,
       }
 
     // organize the sources
-    std::vector<cmSourceFile*> const &classes = cmtarget.GetSourceFiles();
+    std::vector<cmSourceFile*> classes = cmtarget.GetSourceFiles();
+    std::sort(classes.begin(), classes.end(), cmSourceFilePathCompare());
+
     std::vector<cmXCodeObject*> externalObjFiles;
     std::vector<cmXCodeObject*> headerFiles;
     std::vector<cmXCodeObject*> resourceFiles;