There is an LLVM regression that breaks some `f16`-related code when
`fp-armv8` is disabled [1]. Since Rust ties that feature to `neon`,
disable `f16` if `neon` is not available.
[1]: https://github.com/llvm/llvm-project/issues/129394
`compiler_builtins` fails to compile to amdgpu if f128 is enabled.
The reason seems to be that compiler_builtins uses libcalls in the
implementation. I’m not really familiar with what libcalls are, but the
LLVM amdgpu backend explicitly does not support them.
Error message:
```
LLVM ERROR: unsupported libcall legalization
```
Disable `f161` for LoongArch64 due to incorrect code generation on LLVM 19,
which causes failures in `testcrate/tests/conv.rs`. This workaround will
remain in place until llvm/llvm-project#109093 is merged or we upgrade to
LLVM 20.
Make the following changes:
- Add `rerun-if-changed` to the new `configure.rs`, it seems this was
causing incorrect caching.
- Change from matching `i686` to `x86`. The target triple starts with
`i686` so that is what we were checking before, but the architecture
is `x86`. This change should have been made when we added `struct
Target`, update it now instead.
