[PATCH, libstdc++] Fix missing gthr-default.h issue on libstdc++ configure

[Benjamin Kosnik]

> I'd like to know if my direction is ok. I can look into other issues
> releated to this and fix them, but it doesn't make much sense if
> separate build is not supported and can be easily broken in the
> future.

I like your direction here.

> This patch is enough for 4.7 to have build working (at least in
> Android environment).

Confirmed.

> Is it ok for release it into trunk and 4.7?

Yes, please do so.

> I'll take care of remaining trunk issues with other patches if
> necessary.

Great. I just tested your patch on trunk, and despite what I said
yesterday, it seems to work.

-benjamin