[scudo][standalone] 32-bit improvement

Summary:
This tweaks some behaviors of the allocator wrt 32-bit, notably
tailoring the size-class map.

I had to remove a `printStats` from `__scudo_print_stats` since when
within Bionic they share the same slot so they can't coexist at the
same time. I have to find a solution for that later, but right now we
are not using the Svelte configuration.

Reviewers: rengolin

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D74178