Enable leak sanitizer test case

[tmiasko]

• Use black_box to avoid memory leak removal during optimization.
• Leak multiple objects to make test case more robust.

[rust-highfive]

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[alexcrichton]

@bors: r+

[bors]

📌 Commit 8b341e4c539d4876fd34a303ee175189f114248b has been approved by alexcrichton

[Centril]

So I think we might reach the conclusion that because this is 1) in our own test suite under our control and 2) compiled with a toolchain we also fully control, that relying on this might be OK for internal purposes. That said, we currently state that:

Note however, that black_box is only (and can only be) provided on a "best-effort" basis. The extent to which it can block optimisations may vary depending upon the platform and code-gen backend used. Programs cannot rely on black_box for correctness in any way.

So I would like to hear from more folks first (such as e.g. @rkruppe and @RalfJung) to develop a common understanding of our policy here.

For now I will temporarily @bors r-

[alexcrichton]

This is fixing a test and I don't want to deal with policies of using black_box, so

r? @Centril

[Centril]

@bors r+

[bors]

📌 Commit 5d00b5c has been approved by Centril