[sanitizer] Allow for the allocator "names" to be set by the tools

Summary:
In the same spirit of SanitizerToolName, allow the Primary & Secondary
allocators to have names that can be set by the tools via PrimaryAllocatorName
and SecondaryAllocatorName.

Additionally, set a non-default name for Scudo.

Reviewers: alekseyshl, vitalybuka

Reviewed By: alekseyshl, vitalybuka

Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D45600

llvm-svn: 330055