[fixincludes] Fix macOS 10.12 <AvailabilityInternal.h> and <os/trace.h> (PR sanitizer/78267)

[Rainer Orth]

Hi Jack,

> On darwin15, the proposed patch is insufficient to restore the bootstrap
> (after running genfixes in the fixincludes directory) unless I also apply
> the previously proposed change...

no wonder: it's only been tested on darwin16.  Care to explain what
error you're seeing?

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University