[scudo] Enabling AArch64 support for Scudo

Summary:
Adding ARM64 as a supported architecture for Scudo.
The random shuffle is not yet supported for SizeClassAllocator32, which is used
by the AArch64 allocator, so disable the associated test for now.

Reviewers: kcc, alekseyshl, rengolin

Reviewed By: rengolin

Subscribers: aemerson, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D28960

llvm-svn: 293068