[scudo] Attempt to re-enable the valloc test on armhf

Summary:
It used to fail on the bots, but I could not repro it locally. So turn it back
on to try and see if it still fails and maybe get to the heart of it.

Reviewers: alekseyshl, flowerhack

Reviewed By: alekseyshl

Subscribers: aemerson, srhines, kristof.beyls, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D41707