fix Issue 22833 - [REG 2.083] error: 'string' is not a member of 'std'

[ibuclaw]

The foo14 and foo15 C++ tests are linux-only, so it is pointless for OSX, FreeBSD, and Dragonfly to also compile the code where #include <string> was found.

[dlang-bot]

Thanks for your pull request, @ibuclaw!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22833	regression	[REG 2.083] error: 'string' is not a member of 'std'

⚠️⚠️⚠️ Warnings ⚠️⚠️⚠️

• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

To target stable perform these two steps:

1. Rebase your branch to upstream/stable:

git rebase --onto upstream/stable upstream/master

2. Change the base branch of your PR to stable

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#13739"