Another proposal to use RAII rather than __try/__catch block.

libstdc++: [_Hashtable] Use RAII type to guard node while constructing value

libstdc++-v3/ChangeLog:

         * include/bits/hashtable_policy.h
         (struct _NodePtrGuard<_HashtableAlloc, _NodePtr>): New.
         (_ReuseAllocNode::operator()(_Args&&...)): Use latter to guard 
allocated node
         pointer while constructing in place the value_type instance.

Tested under Linux x64, ok to commit ?

François