Ensure pool resources always use normal mode vector

The __pool_resource::_M_unpooled member was declared with type
std::vector, which means that the type depends on whether debug mode is
active or not. Because the non-inline definitions in
src/c++17/memory_resource.cc are never compiled with debug mode, the
type declared in the header doesn't match the type in the library
definitions, leading to undefined behaviour.

The solution is to ensure the header always uses the non-debug vector,
even when debug mode is active. To make this easier a new alias template
is defined: _GLIBCXX_STD_C::pmr::vector.

	* include/std/memory_resource (__pool_resource::_M_unpooled): Use
	normal mode vector, even for debug mode.
	* include/std/vector [_GLIBCXX_DEBUG] (_GLIBCXX_STD_C::pmr::vector):
	Define alias template for normal mode vector.

From-SVN: r268354

libstdc++-v3/ChangeLog

+2019-01-29  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/memory_resource (__pool_resource::_M_unpooled): Use
+	normal mode vector, even for debug mode.
+	* include/std/vector [_GLIBCXX_DEBUG] (_GLIBCXX_STD_C::pmr::vector):
+	Define alias template for normal mode vector.
+
 2019-01-28  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/68737

libstdc++-v3/include/std/memory_resource

@@ -354,7 +354,7 @@ namespace pmr
     struct _BigBlock;
     // Collection of blocks too big for any pool, sorted by address.
     // This also stores the only copy of the upstream memory resource pointer.
-    pmr::vector<_BigBlock> _M_unpooled;
+    _GLIBCXX_STD_C::pmr::vector<_BigBlock> _M_unpooled;
 
     const int _M_npools;
   };

libstdc++-v3/include/std/vector

@@ -89,6 +89,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _Tp>
       using vector = std::vector<_Tp, polymorphic_allocator<_Tp>>;
   } // namespace pmr
+# ifdef _GLIBCXX_DEBUG
+  namespace _GLIBCXX_STD_C::pmr {
+    template<typename _Tp>
+      using vector
+	= _GLIBCXX_STD_C::vector<_Tp, std::pmr::polymorphic_allocator<_Tp>>;
+  } // namespace _GLIBCXX_STD_C::pmr
+# endif
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
 #endif // C++17