bct_p *is* used in loop.c:strength_reduction

[David Edelsohn]

`unused'
     This attribute, attached to a variable, means that the variable is
     meant to be possibly unused.  GNU CC will not produce a warning
     for this variable.

I do not know what "meant to be possibly" is intended to convey.  This is
intended for cases where some compilations will not use the variable?

David