[compiler-rt] [scudo] Add config option to modify get usable size behavior (PR #158710)

[via llvm-commits]

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ChiaHungDuan wrote:

Just some minor comment (it's not necessary to take the suggestions here)

I'm thinking if we can do/simplify the test like

1. Iterate the size class map and allocate a fixed size if it's greater than the size class
2. Verify p + usable_size <= end of block
3. I think this can be done in primary_test.cpp

We don't test different alignments or some random sizes because I think 2. is enough for the usable size 

https://github.com/llvm/llvm-project/pull/158710