BuildArchitectures: and default

["H. Peter Anvin" <hpa zytor com>]

I have a package which produces both architecture-dependent and 
architecture-independent output.  I'd like to produce both a noarch 
package as well as whatever the "usual" architecture (either the default 
or provided via --target).

Is there a macro or something that reflects what the "standard" value of 
BuildArchitectures would have been, so I can do something like:

BuildArchitectures: noarch %{_target_arch}

(It would still be nicer if a single pass could produce all 
architectures, but the equivalent of the above seem to work if I 
hard-code the architecture.)

	-hpa