r242293 - Set comdat when an available_externally thunk is converted to linkonce_odr.

[John McCall]

> On Jul 15, 2015, at 1:37 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> Looks good to me, but John's the code owner for IR generation so I'd like his signoff.

LGTM.

John.