mio ac5de49282 main/rust-bindgen: build with non-default clang ...

Building with clang 21 results in the failed tests below. Temporarily
rebuild with clang 20 for now.

```
failures:

---- header_issue_544_stylo_creduce_2_hpp stdout ----
diff expected generated
--- expected: "/home/buildozer/aports/main/rust-bindgen/src/rust-bindgen-0.72.1/bindgen-tests/tests/expectations/tests/issue-544-stylo-creduce-2.rs"
[...]
thread 'header_issue_544_stylo_creduce_2_hpp' panicked at /home/buildozer/aports/main/rust-bindgen/src/rust-bindgen-0.72.1/target/debug/build/bindgen-tests-9de8543d86140b47/out/tests.rs:394:1:
Header and binding differ! Run with BINDGEN_OVERWRITE_EXPECTED=1 in the environment to automatically overwrite the expectation or with BINDGEN_TESTS_DIFFTOOL=meld to do this manually.

[...]

failures:
    header_issue_544_stylo_creduce_2_hpp
    header_nsbasehashtable_hpp
```

2025-10-18 20:43:11 +00:00

..

APKBUILD

…

disable-test_wrap_static_fns-patch

…