[Bug libstdc++/59656] weak_ptr::lock function crashes when compiling with -fno-exceptions flag

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59656

--- Comment #7 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
Created attachment 31924
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31924&action=edit
Alternate fix from Kyle Lippincott

Alternate patch, courtesy Kyle Lippincott <spectral@google.com>.

AFAIU, Kyle's patch uses roughly the same idea as Jonathan's,
but no #ifdef's.

Should we take these patches to gcc-patches list?