Follow-up to commit 3e1e73fc
"build: Check for cargo when building rust language":

On 2024-04-15T13:14:42+0200, I wrote:
> I now wonder: instead of 'AC_CHECK_TOOL', shouldn't this use
> 'AC_CHECK_PROG'?  (We always want plain 'cargo', not host-prefixed
> 'aarch64-linux-gnu-cargo' etc., right?)  I'll look into changing this.

	* configure: Regenerate.
	config/
	* acx.m4 (ACX_PROG_CARGO): Use 'AC_CHECK_PROGS'.