Add LTO visibility attribute for wait_context_vertex

[kboyarinov]

Description

Fixes # - issue number(s) if exists

Type of change

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• [ ] bug fix - change that fixes an issue
• [ ] new feature - change that adds functionality
• [ ] tests - change in tests
• [ ] infrastructure - change in infrastructure and CI
• [ ] documentation - documentation update

Tests

• [ ] added - required for new features and some bug fixes
• [ ] not needed

Documentation

• [ ] updated in # - add PR number
• [ ] needs to be updated
• [ ] not needed

Breaks backward compatibility

• [ ] Yes
• [ ] No
• [ ] Unknown

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Other information

[solbjorn]

Pinging just in case.

I've been using changes from this PR for 1.5 months already with no issues observed (with -fwhole-program-vtables enabled for both oneTBB and my app).

My app is only a home project, no urgency anyway.