Comment 5 for bug 633673

(In reply to comment #3)
> src.rpm headers have always been architecture specific, nothing new here. Its
> just that using %{_isa} in BuildRequires just makes it more visible than
> before.
>
> There's nothing (well, except possible distro-specific packaging policies)
> stopping people from using something like (just an artificial example):
> BuildRequires: %{_libdir}/tclConfig.sh
> ..which would end up in src.rpm requires as /usr/lib/tclConfig.sh or
> /usr/lib64/
> tclConfig.sh depending on which architecture the src.rpm happened to be created
> on. Or conditional buildrequires like
> %ifarch %{x86}
> BuildRequires: foo
> %endif

Yes, but all except the last are pointless unless they're evaluated at *build* time, not SRPM creation time.

Really, if you're adding %{_isa} to build requires, it's not that you actually care at all what the value of %{_isa} is; you just care it's the same for all the packages you're attaching it to. Hence, setting the value in the source rpm seems wrong.