[TargetLowering] Check boolean content when folding bit compare

Updates an optimization that relies on boolean contents being either 0
or 1 to properly check for this before triggering.

The following:
  (X & 8) != 0 --> (X & 8) >> 3
Produces unexpected results when a boolean 'true' value is represented
by negative one.

Patch by Erik Hogeman.

Differential Revision: https://reviews.llvm.org/D89390