do not fail if prctl is not allowed

[ekrasikov]

Changelog category (leave one):

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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

• do not fail if prctl() syscall is not allowed (e.g. in AWS Lambda)

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

see this or this for details

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✅ ekrasikov
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