AK: `AK::Detail::VisitImpl::has_explicitly_named_overload` causes ICE in clang assertions build

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This has been a thing since at least spring 2022, when clang trunk was clang-15(?).

https://github.com/llvm/llvm-project/issues/53815

This issue was reduced by @mjz19910 from AK::Variant back in the day.

Currently it's causing fun times for the FreeBSD CI that their port of Ladybird is running.

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=276703

It still repros on trunk (https://github.com/llvm/llvm-project/commit/bc6b5be6a298ab094d1bb41f393ca422feddd298)

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cc @clausecker

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An LLVM PR was created that should resolve this on trunk. Not sure if it'll end up getting back ported to the 18 release branch -- we could always ask after it's reviewed/merged.

https://github.com/llvm/llvm-project/pull/83103

[clausecker]

This is a known issue; the port is currently marked as BROKEN on FreeBSD 15-CURRENT for this reason.