Rollup merge of #143125 - tgross35:aarch64-neon-llvm19-f16, r=cuviper

Disable f16 on Aarch64 without neon for llvm < 20.1.1

This check was added unconditionally in c51b229 ("Disable f16 on Aarch64 without `neon`") and reverted in 4a8d357 ("Revert "Disable `f16` on Aarch64 without `neon`"") since it did not fail in Rust's build. However, it is still possible to hit this crash if using LLVM 19 built with assertions, so disable the type conditionally based on version here.

Note that for these builds, a similar patch is needed in the build script for `compiler-builtins` since it does not yet use `cfg(target_has_reliable_f16)` (hopefully to be resolved in the near future).

Report: rust-lang/rust#139276 (comment)
Original LLVM issue: llvm/llvm-project#129394

Author: matthiaskrgr