Desugar class type for iterator lookup.

[saugustine]

Summary

Without this, printing sets and maps hidden behind
using declarations fail.

libcxx/test/pretty_printers/gdb_pretty_printer_test.sh.cpp

ComparePrettyPrintToChars(one_two_three,
       "std::set with 3 elements = {1, 2, 3}");
 
   std::set<std::pair<int, int>> prime_pairs {
       std::make_pair(3, 5), std::make_pair(5, 7), std::make_pair(3, 5)};
 
   ComparePrettyPrintToChars(prime_pairs,
       "std::set with 2 elements = {"
       "{first = 3, second = 5}, {first = 5, second = 7}}");
+
+  using using_set = std::set<int>;
+  using_set other{1, 2, 3};
+  ComparePrettyPrintToChars(other, "std::set with 3 elements = {1, 2, 3}");
 }
 
 void stack_test() {
   std::stack<int> test0;
   ComparePrettyPrintToChars(test0,
                             "std::stack wrapping = {std::deque is empty}");
   test0.push(5);
   test0.push(6);

libcxx/utils/gdb/libcxx/printers.py

def to_string(self):
         return "%s is empty" % typename
 
 
 class StdMapPrinter(AbstractRBTreePrinter):
     """Print a std::map or std::multimap."""
 
     def _init_cast_type(self, val_type):
         map_it_type = gdb.lookup_type(
-            str(val_type) + "::iterator").strip_typedefs()
+            str(val_type.strip_typedefs()) + "::iterator").strip_typedefs()
         tree_it_type = map_it_type.template_argument(0)
         node_ptr_type = tree_it_type.template_argument(1)
         return node_ptr_type
 
     def display_hint(self):
         return "map"
 
     def _get_key_value(self, node):
         key_value = node.cast(self.util.cast_type).dereference()[
             "__value_"]["__cc"]
         return [key_value["first"], key_value["second"]]
 
 
 class StdSetPrinter(AbstractRBTreePrinter):
     """Print a std::set."""
 
     def _init_cast_type(self, val_type):
         set_it_type = gdb.lookup_type(
-            str(val_type) + "::iterator").strip_typedefs()
+            str(val_type.strip_typedefs()) + "::iterator").strip_typedefs()
         node_ptr_type = set_it_type.template_argument(1)
         return node_ptr_type
 
     def display_hint(self):
         return "array"
 
     def _get_key_value(self, node):
         key_value = node.cast(self.util.cast_type).dereference()["__value_"]