[Infra] Clang Support

[yurivict]

Log: https://people.freebsd.org/~yuri/seqan3-tests.log

[marehr]

Hi yurivict,

we don't support clang at the moment, as we have written in https://github.com/seqan/seqan3/blob/master/README.md#dependencies.

We have a progress ticket seqan/product_backlog#127 that tracks the progress and open bug tickets considering clang.

For example: clang does not support including the header #include <ranges> (see https://godbolt.org/z/rsKsPsWxE) from the gcc stdlib. We are working on that, but it will take some time.

Our goal is to support all C++20 compiler, but right now, only gcc supports the subset that we need.

[eseiler]

Currently, this issue is blocking: llvm/llvm-project#56394

[eseiler]

We now support clang 17 on the master branch (via #3195).