[NFC][CodeGen][SelectionDAG] Tests for X % C == 0 codegen improvement.

Hacker's Delight 10-17: when C is constant,
the result of X % C == 0 can be computed more cheaply
without actually calculating the remainder.

The motivation is discussed here:
https://bugs.llvm.org/show_bug.cgi?id=35479.

Patch by: hermord (Dmytro Shynkevych)!

For https://reviews.llvm.org/D50222

llvm-svn: 341047