[patch] PR/99296: Handle setting of 1-bit anti-ranges uniformly

[Aldy Hernandez]

Creation of inverse ranges in the irange code was not dealing with 
signed 1-bit quantities correctly.

The legacy code had special cased this case, so I adapted and pulled out 
some code to do it in one place.

Could someone double check the logic here, please?

Thanks.
Aldy
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