[NFC][IndVarSimplify] Test: replacing IV user with unsafe loop-invariant (PR45360)

https://bugs.llvm.org/show_bug.cgi?id=45360

This is reduced from the (runnable) test provided in the bug report.
The remainder operation is originally guarded, it never divides by zero.
Indvars should not make it execute unconditionally.

This is not a great test, running whole -O2 is fragile,
but i really don't understand why running -indvars on the IR before
that tranform happens doesn't work.