[compiler-rt] [scudo][NFC] Add a default unmap() to unmap all pages (PR #102234)

[Christopher Ferris via llvm-commits]

https://github.com/cferris1000 approved this pull request.

Assuming my question about the two test cases that use Size instead of the capacity value are actually an error.

https://github.com/llvm/llvm-project/pull/102234