gh-37646: Fix compilation with -std=c++17
<!-- ^ Please provide a concise and informative title. -->
<!-- ^ Don't put issue numbers in the title, do this in the PR
description below. -->
<!-- ^ For example, instead of "Fixes #12345" use "Introduce new method
to calculate 1 + 2". -->
<!-- v Describe your changes below in detail. -->
<!-- v Why is this change required? What problem does it solve? -->
<!-- v If this PR resolves an open issue, please link to it here. For
example, "Fixes #12345". -->
Fixes https://github.com/sagemath/sage/issues/36840.
0c96d61fb0f908ca43cede20b20224fb635da176: I don't think there should be
any issues with this, as it should be exactly what `cpdef` does under
the hood. That being said, I'd like someone knowledgable with Cython to
sanity check this.
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. -->
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.
### :hourglass: Dependencies
<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
N/A
URL: https://github.com/sagemath/sage/pull/37646
Reported by: Shorden
Reviewer(s): Matthias Köppe, Shorden
Committer
Release Manager
