fix for execute/991221-1.c -O1 failure

[Martin v. Loewis]

> Here is the pointerized version of 991221.c .
> I know this is not standard C, but I suppose gcc should be able to handle
> this.  N.B. it works with -O0 but fails when optimizing.
> 
> gcc itself uses -1 as a special 'pointer' value in some places.

I agree this test should pass. I'm not so sure that gcc should perform
the range folding. Couldn't it just avoid the folding if the arguments
in the relative operator are pointer literals?

Regards,
Martin