fn find_php() -> Result<PathBuf> {
    // If path is given via env, it takes priority.
    if let Some(path) = path_from_env("PHP") {
        if !path.try_exists()? {
            // If path was explicitly given and it can't be found, this is a hard error
            bail!("php executable not found at {:?}", path);
        }
        return Ok(path);
    }
    find_executable("php").with_context(|| {
        "Could not find PHP executable. \
        Please ensure `php` is in your PATH or the `PHP` environment variable is set."
    })
}
Finds the location of the PHP executable.
build.rs