Adding a new thread model to GCC

[Eric Botcazou]

> The libgcc parts look reasonable to me, but I can't approve them.
> Maybe Jonathan Yong can approve those parts as mingw-w64 target
> maintainer, or maybe a libgcc approver can do so.

OK.

> The libstdc++ parts are OK for trunk. IIUC they could go in
> separately, they just wouldn't be very much use without the libgcc
> changes.

Sure thing.

-- 
Eric Botcazou