GDB pretty printer

GDB pretty printing does not work for various STL containers.

Steps to reproduce:
* debug [SampleCode/Cxx11SGXDemo](https://github.com/intel/linux-sgx/tree/master/SampleCode)
* set breakpoint to [Enclave/TrustedLibrary/Libcxx.cpp](https://github.com/intel/linux-sgx/blob/master/SampleCode/Cxx11SGXDemo/Enclave/TrustedLibrary/Libcxx.cpp#L72) line 72
```c++
70: // Sample usages for lamdbas:
71: std::vector< int> v { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
72: printf("[Lambdas] Initial array using lambdas: { ");
73:
```
* print previously defined variable v (gdb: `print v`)

result:

`$1 = { >> = {> = {}, __begin_ = 0x7ffff4294070, __end_ = 0x7ffff429409c, __end_cap_ = {, 2u>> = {> = {}, __first_ = 0x7ffff429409c}, }}, }`

`info pretty-printer` returns:

```
global pretty-printers:
builtin
mpx_bound128
objfile /usr/lib/x86_64-linux-gnu/libstdc++.so.6 pretty-printers:
libstdc++-v6
__gnu_cxx::_Slist_iterator
__gnu_cxx::__7::_Slist_iterator
__gnu_cxx::__7::__normal_iterator
__gnu_cxx::__7::slist
__gnu_cxx::__normal_iterator
__gnu_cxx::slist
__gnu_debug::_Safe_iterator
std::_Deque_const_iterator
std::_Deque_iterator
std::_List_const_iterator
std::_List_iterator
std::_Rb_tree_const_iterator
std::_Rb_tree_iterator
std::__7::_Deque_const_iterator
std::__7::_Deque_iterator
std::__7::_List_const_iterator
std::__7::_List_iterator
std::__7::_Rb_tree_const_iterator
std::__7::_Rb_tree_iterator
std::__7::__cxx11::basic_string
std::__7::basic_string
std::__7::bitset
std::__7::deque
std::__7::forward_list
std::__7::list
std::__7::map
std::__7::multimap
std::__7::multiset
std::__7::priority_queue
std::__7::queue
std::__7::set
std::__7::shared_ptr
std::__7::stack
std::__7::tuple
std::__7::unique_ptr
std::__7::unordered_map
std::__7::unordered_multimap
std::__7::unordered_multiset
std::__7::unordered_set
std::__7::vector
std::__7::weak_ptr
std::__cxx11::basic_string
std::__cxx1998::_Deque_const_iterator
std::__cxx1998::_Deque_iterator
std::__cxx1998::_List_const_iterator
std::__cxx1998::_List_iterator
std::__cxx1998::__7::_Deque_const_iterator
std::__cxx1998::__7::_Deque_iterator
std::__cxx1998::__7::_List_const_iterator
std::__cxx1998::__7::_List_iterator
std::__cxx1998::__7::bitset
std::__cxx1998::__7::deque
std::__cxx1998::__7::forward_list
std::__cxx1998::__7::list
std::__cxx1998::__7::map
std::__cxx1998::__7::multimap
std::__cxx1998::__7::multiset
std::__cxx1998::__7::set
std::__cxx1998::__7::unordered_map
std::__cxx1998::__7::unordered_multimap
std::__cxx1998::__7::unordered_multiset
std::__cxx1998::__7::unordered_set
std::__cxx1998::__7::vector
std::__cxx1998::bitset
std::__cxx1998::deque
std::__cxx1998::forward_list
std::__cxx1998::list
std::__cxx1998::map
std::__cxx1998::multimap
std::__cxx1998::multiset
std::__cxx1998::set
std::__cxx1998::unordered_map
std::__cxx1998::unordered_multimap
std::__cxx1998::unordered_multiset
std::__cxx1998::unordered_set
std::__cxx1998::vector
std::__debug::bitset
std::__debug::deque
std::__debug::forward_list
std::__debug::list
std::__debug::map
std::__debug::multimap
std::__debug::multiset
std::__debug::priority_queue
std::__debug::queue
std::__debug::set
std::__debug::stack
std::__debug::unique_ptr
std::__debug::unordered_map
std::__debug::unordered_multimap
std::__debug::unordered_multiset
std::__debug::unordered_set
std::__debug::vector
std::__norm::_Deque_const_iterator
std::__norm::_Deque_iterator
std::__norm::_List_const_iterator
std::__norm::_List_iterator
std::basic_string
std::bitset
std::deque
std::experimental::filesystem::v1::__7::path
std::experimental::filesystem::v1::__cxx11::__7::path
std::experimental::filesystem::v1::__cxx11::path
std::experimental::filesystem::v1::path
std::experimental::fundamentals_v1::__7::any
std::experimental::fundamentals_v1::__7::basic_string_view
std::experimental::fundamentals_v1::__7::optional
std::experimental::fundamentals_v1::any
std::experimental::fundamentals_v1::basic_string_view
std::experimental::fundamentals_v1::optional
std::forward_list
std::list
std::map
std::multimap
std::multiset
std::priority_queue
std::queue
std::set
std::shared_ptr
std::stack
std::tr1::__7::shared_ptr
std::tr1::__7::unordered_map
std::tr1::__7::unordered_multimap
std::tr1::__7::unordered_multiset
std::tr1::__7::unordered_set
std::tr1::__7::weak_ptr
std::tr1::shared_ptr
std::tr1::unordered_map
std::tr1::unordered_multimap
std::tr1::unordered_multiset
std::tr1::unordered_set
std::tr1::weak_ptr
std::tuple
std::unique_ptr
std::unordered_map
std::unordered_multimap
std::unordered_multiset
std::unordered_set
std::vector
std::weak_ptr
```

I am using `sgx-gdb` (`gdb 7.11.1`) on ubuntu 16.04. My SGX SDK repo is on 0f45cad401e974bee57704f3fb0ff185146bbde2 but all changes since then should not have an impact on the gdb pretty printers.