Env - deps`arborium` build failed

## Description

Using `dioxus-code` in a Dioxus web application causes the WASM build
to compile `arborium-sysroot`.

On macOS, the default Apple Clang does not include the WebAssembly
backend, so `dx serve` fails unless `CC` and `CXX` are explicitly set
to a Homebrew LLVM installation.

---
## Reproduction

Cargo.toml:
```toml
[dependencies]
dioxus = "0.7"
dioxus-code = "0.1"
```
Then run:
```bash
dx serve
```
---
## Environment

- macOS
- Apple Clang
- dioxus-code 0.1.2
- target: wasm32-unknown-unknown

---
## Output

```bash
[cargo] error: failed to run custom build command for `arborium-sysroot v2.18.1`
[cargo] Caused by:
...
[cargo] cargo:warning=error: unable to create target: 'No available targets are compatible with triple "wasm32-unknown-unknown"'
```

Start with the dependency declarations in Cargo.toml and reproduce the failure with dx serve for a wasm32-unknown-unknown target. Read the arborium-sysroot v2.18.1 build output and compare how CC and CXX are handled on macOS; done means the documented reproduction builds without the Apple Clang WebAssembly-target error.

Written by the indexing model from the issue text.