P0767R1: Deprecate POD

[ldionne]

Link: https://wg21.link/P0767R1

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It was previously erroneously marked as complete in LLVM 7.
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[ldionne]

This issue has already been implemented and was created for tracking purposes only.

[llvmbot]

@llvm/issue-subscribers-c-20

Author: Louis Dionne (ldionne)

**Link:** https://wg21.link/P0767R1

[frederick-vs-ja]

It's doubtful whether this is implemented in LLVM 7 as we haven't added corresponding deprecation warnings.

Edit: Resolved in #129471.