Recognize XOR-based periodic induction.

Rationale:
This is a commonly used construct (e.g. x = !x for booleans
and x ^= 1 for integers). This CL prepares some upcoming
optimizations that exploit such inductions.

Change-Id: I46edffb9de1075a836995daf5c2dfff7891f3034
Test: 530-checker-loops2 and induction_var_analysis_test