[compiler-rt] [scudo] change allocation buffer size with env var (PR #71703)

[Florian Mayer via llvm-commits]

fmayer wrote:

> Is there any problem if this value is set negative or set to a really large positive value?
> 
> I want to make sure there is no possibility that a value here can cause a segfault.

The negative value is addressed in this: https://github.com/llvm/llvm-project/pull/71791

The (too) large positive value will lead to a crash, because mmap will fail and crash (we don't pass `MAP_ALLOWNOMEM`)

https://github.com/llvm/llvm-project/pull/71703