On x86_64, the `@divFloor` change is a strict improvement, and the
`@mod` change adds one zero latency instruction.  In return, once we
upgrade to LLVM 20, when the optimizer discovers one of these operations
has a power-of-two constant rhs, it will be able to optimize the entire
operation into an `ashr` or `and`, respectively.

                      #I   CPL   CPT
    old `@divFloor` |  8 | 15 | .143 |
    new `@divFloor` |  7 | 15 | .148 |
    old `@mod`      |  9 | 17 | .134 | (rip llvm
    new `@mod`      | 10 | 17 | .138 |  scheduler)