[SCEV] Don't crash on pointer comparisons

`ScalarEvolution::isImpliedCondOperandsViaNoOverflow` tries to cast the
operand type of the comparison it is given to an `IntegerType`.  This is
incorrect because it could actually be simplifying a comparison between
two pointers.  Switch it to using `getTypeSizeInBits` instead, which
does the right thing for both pointers and integers.

Fixed PR24956.

llvm-svn: 248743