32-bit test failure in core, box: argument is of incorrect size

On 32 bit Windows since 07780c24f48172b088fd6, running `test/core.jl` gives `ERROR: box: argument is of incorrect size` at line 1138. Oddly in the REPL, running these lines gives `ERROR: type: apply: expected Function, got IntrinsicFunction` instead.

I don't entirely get what `Intrinsics.box` does, so this could easily be breaking the intent of these tests for issues #4581 and #6591, not sure. Any better fixes for this problem?

Don't have a 32 bit Linux machine to test on, but I suspect this may be causing similar issues there?