python-cryptography: Fix LTO/Rust symbol relocation issues

Describe the bug

python-cryptography 41.0.0+ fails to load with "Error relocating: PyInit__openssl: symbol not found" when built with GCC LTO. This is due to interaction between GCC's LTO and Rust compilation.

OpenWrt version

r0-685e979d4

OpenWrt release

SNAPSHOT

OpenWrt target/subtarget

x86/64

Device

PC Engines apu2

Image kind

Self-built image

Steps to reproduce

1. Install python3-cryptography
2. Try to import cryptography in Python or use any application that depends on it
3. Get ImportError: Error relocating /usr/lib/python3.11/site-packages/cryptography/hazmat/bindings/_rust.abi3.so: PyInit__openssl: symbol not found

Actual behaviour

Python module fails to load with symbol relocation errors

Expected behaviour

Python module loads successfully

Additional info

This is a known upstream issue: https://github.com/pyca/cryptography/issues/9023

The fix is to use clang/lld for compilation instead of GCC, as this provides proper integration between Rust and C parts of the module.

Applied fix:

• Use clang/lld toolchain
• Set appropriate RUSTFLAGS for proper LTO between Rust and clang components

Diffconfig

N/A - Package fix only

Terms

• I am reporting an issue for OpenWrt, not an unsupported fork.

Start with the python3-cryptography package build definition and reproduce the failure by importing cryptography on the reported OpenWrt snapshot. Review upstream issue 9023 and the described clang/lld and RUSTFLAGS approach; the work is done when the module imports successfully without the PyInit__openssl relocation error.