cmListFileContext: Sort by line before file.

This should be much faster.  In the context where it is used the
line comparison should be sufficient, removing the need to compare
files at all.

Source/cmListFileCache.cxx

@@ -434,8 +434,9 @@ std::ostream& operator<<(std::ostream& os, cmListFileContext const& lfc)
 
 bool operator<(const cmListFileContext& lhs, const cmListFileContext& rhs)
 {
-  if(lhs.FilePath != rhs.FilePath)
-    return lhs.FilePath < rhs.FilePath;
-
-  return lhs.Line < rhs.Line;
+  if(lhs.Line != rhs.Line)
+    {
+    return lhs.Line < rhs.Line;
+    }
+  return lhs.FilePath < rhs.FilePath;
 }