[hwasan] Switch to 64 allocator with a dense size class map.

Summary:
Replace the 32-bit allocator with a 64-bit one with a non-constant
base address, and reduce both the number of size classes and the maximum
size of per-thread caches.

As measured on [1], this reduces average weighted memory overhead
(MaxRSS) from 26% to 12% over stock android allocator. These numbers
include overhead from code instrumentation and hwasan shadow (i.e. not a
pure allocator benchmark).

This switch also enables release-to-OS functionality, which is not
implemented in the 32-bit allocator. I have not seen any effect from
that on the benchmark.

[1] https://android.googlesource.com/platform/system/extras/+/master/memory_replay/

Reviewers: vitalybuka, kcc

Subscribers: kubamracek, cryptoad, llvm-commits

Differential Revision: https://reviews.llvm.org/D56239

llvm-svn: 350370