Error building on cmake 4.1.2 (outdated zstd used by ccache)

Error:

```
CMake Error at /Users/m1/pyodide_env/pyodide/emsdk/emsdk/ccache/git-emscripten_64bit/build_emscripten_64/zstd-1.4.8/build/cmake/CMakeLists.txt:10 (cmake_minimum_required):
Compatibility with CMake < 3.5 has been removed from CMake.

Update the VERSION argument value. Or, use the ... syntax
to tell CMake that the project requires at least but has been updated
to work with policies introduced by or earlier.

Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.
```

Apparently because buid is using https://github.com/juj/ccache which is still relying on zstd 1.4.8 and downloading it from the internet.

https://github.com/juj/ccache/blob/c4284c78e9ff286ee5208f449af4c2aaba062d37/cmake/Findzstd.cmake#L9

zstd 1.4.8:
https://github.com/facebook/zstd/blob/v1.4.8/build/cmake/CMakeLists.txt#L10

The first zstd version that has cmake 3.5+ is 1.5.6:
https://github.com/facebook/zstd/blob/v1.5.6/build/cmake/CMakeLists.txt#L10