Bug#1113237: llvm-toolchain-19: FTBFS with CMake 4

[Timo Röhling]

Hello again,

On Sat, 22 Nov 2025 00:12:13 +0100 Timo =?utf-8?Q?R=C3=B6hling?= 
> The actual bug is that LLVM {17,18,19} try to build shared libraries 
> for WebAssembly, which does not support them. CMP0164 [1] turned this 
> into a fatal error, and CMake 4 implicitly activates this policy in 
> export files [2], which is why this became a FTBFS.

I've looked into this a bit further and found an upstream issue [1].
In the pull request trying to fix it, upstream notes that you need to 
enable shared libraries explicitly (which is what Debian does), so this 
actually needs to be fixed by whoever builds for the wasm32 target [2].

My first instinct was to look at the build-wasm/compiler-rt-%" targets 
in debian/rules, but I could not determine where the shared library 
build is actually activated. Hopefully, someone with a better grasp of 
the codebase can pick it up from here.


Cheers
Timo

[1] https://github.com/llvm/llvm-project/issues/118048
[2] 
https://github.com/llvm/llvm-project/pull/118262#issuecomment-2561578536
and the follow-up comment


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