Backport revision 180159 to gcc 4.6 branch

[Chase Douglas]

Hi,

I don't really follow gcc much, so I hope I'm asking this in the right
place :).

I would like to ask that the fix in revision 180159 be backported to the
gcc 4.6 branch. It's a trivial change, but without it clang cannot
compile anything using the default std::shared_ptr constructor. That's
my understanding at least, based on what I read at
http://stackoverflow.com/questions/7964360/using-stdshared-ptr-with-clang-and-libstdc.

Please let me know if there's any way I can help.

Thanks!

-- Chase