[scudo][standalone] Unmap memory in tests
The more tests are added, the more we are limited by the size of the
address space on 32-bit. Implement unmapTestOnly all around (like it
is in sanitzer_common) to be able to free up some memory.
This is not intended to be a proper "destructor" for an allocator, but
allows us to not fail due to having no memory left.
Reviewers: morehouse, vitalybuka, eugenis, hctim
Reviewed By: morehouse
Subscribers: delcypher, jfb, #sanitizers, llvm-commits
Tags: #llvm, #sanitizers
Differential Revision: https://reviews.llvm.org/D63146