[compiler-rt] [scudo] Add new fast purge option. (PR #175266)

[Jordan R AW via llvm-commits]

ajordanr-google wrote:

> In some cases, code wants a fast version that releases as fast as possible and the call will not block.

To clarify, you mean block on trying to acquire a lock? Not on blocking while trying to conduct the purge.

> In the future, I envision that this option will also do a calculation to stop purging after some cutoff value to avoid being blocked in this call for too long.

Clarifying, this is about `FastPurge` not `Purge`? `Purge` I would have thought already does this, but may wait on locks, but the description of the PR makes it a little confusing.

https://github.com/llvm/llvm-project/pull/175266