[scudo][standalone] Workaround for full regions on Android

Summary:
Due to Unity, we had to reduce our region sizes, but in some rare
situations, some programs (mostly tests AFAICT) manage to fill up
a region for a given size class.

So this adds a workaround for that attempts to allocate the block
from the immediately larger size class, wasting some memory but
allowing the application to keep going.

Reviewers: pcc, eugenis, cferris, hctim, morehouse

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D74567