When compiling code for a case where the scrutinee is a primitve
comparison operator, we used to place the tag in a variable whose
unique was always the same: `mkPseudoUnique1 1'.  This was mostly
harmless but confused the Stix inliner in the NCG into generating
slightly less efficient code when the variable was used twice in a
basic block.

This patch fixes the problem by generating a new unique by just
changing the "tag" of an existing unique, namely the case binder.