[scudo][standalone] Add bytemap classes

Summary:
The bytemap classes will be used by the primary32 allocator to associate
classes with memory regions. It's similar to the sanitizer_common one
except for the fact that the base (level1) maps are mapped instead of
being static to reduce the memory footprint of an uninitialized allocator.

Reviewers: vitalybuka, eugenis, morehouse, flowerhack, dmmoore415, mcgrathr

Reviewed By: vitalybuka, morehouse

Subscribers: mgorny, delcypher, jfb, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D58723

llvm-svn: 355416