fix issue 20021 - static if doesn't evaluate opCast(bool)

[aG0aep6G]

This is a reboot of #10237 which apparently was ready to go, but @dkorpel encountered problems when rebasing to stable.

[dlang-bot]

Thanks for your pull request and interest in making D better, @aG0aep6G! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20021	regression	static if doesn't evaluate opCast(T : bool)

Testing this PR locally

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

dub fetch digger
dub run digger -- build "stable + dmd#10324"

[dkorpel]

Funny, I was just opening my reboot for this when I saw this popping up.
The tests are failing because the extra line fail_compilation/ice11553.d(22): changes the line number to 23.

[aG0aep6G]

Funny, I was just opening my reboot for this when I saw this popping up.

Great minds think alike, I guess :)
If you want to pursue this yourself, just let me know and I'll close this.