Patch to allow strlen expander to fail

[Jamie Lokier]

Jeffrey A Law wrote:
> The __main is not a hosted vs non-hosted issue -- the behavior of the
> compiler is correct.  __main is critical for the proper behavior of
> ctors/dtors which are 100% independent of the hosted vs non-hosted
> environment.

Does the __main mechanism work at all for a freestanding environment?
Part of the definition of freestanding is that the program isn't
necessarily entered at main.

-- Jamie