In the same naive spirit, I would offer that using the same compiler for building perl and its extensions seems more likely to succeed. If I could reason about symbols and libraries and memory addresses, I would be able to explain why. I know in some ways it isn't especially complicated, but you do need to learn how to reason about it, which is possible only through actually debugging experience, at least for myself.

Tk isn't especially easy to compile. Since so many perl modules are available through Debian, it's a suitable development environment in that it gets you a compiled Tk for free. When I compile Tk for myself, under whichever perl version, I always have to force it to install as there is always a failing test. I just believe and pray I won't touch that code because I never bothered to try and figure it out. Up to now I've been a rather pedestrian user. No nuclear reactors depend on my code!

I'm aware there's another Tk interface for perl, Tkx. I've never touched it, but understand it is closer to Tcl/Tk than the more perlish Tk. Perhaps Tkx will compile and work for your app under clang.