meson: fix build with lld on linux

[natthias]

Currently, building on a system with clang fails with
clang: error: unknown argument: '-export-symbols-regex=^jose_.*'
as they are not 1:1 compatible. This fixes this by explicitly checking for clang and falling back to the FreeBSD check, which also uses clang.

Not sure if this is the correct solution, but jose now successfully builds with both clang and gcc.

[hdholm]

It looks to me like v15 built with clang correctly (see https://github.com/latchset/jose/actions/runs/27129994139 ) Is there some detail I'm missing about the clang build on which you're seeing this?

[natthias]

Ahh yea, a bit too fast there. This is not the fault of clang itself, but rather using lld as the linker instead of bfd. Converting this to a draft as this is definetly not the correct solution.

edit:
Interestingly, gcc only treats ld.lld: warning: cannot find entry symbol xport-symbols-regex=^jose_.*; not setting start address as a warning, and not and error.

[natthias]

Yea, so the issue seems to be exactly what the freebsd faced in #152.
Perhaps checking for lld and then falling back to the --undefined-version invocation is a more scalable solution going forward?

[natthias]

Now explicitly checks for lld instead of clang.