Joshua A Clayton authored Feb 19, 2015 and Brad King committed Feb 23, 2015

BuildArch must only be added to a spec file for a "noarch" package or
rpmbuild will fail.  For all others, the --target argument sets the
package architecture.  In the process of Fixing rpm architecture, we
make it mandatory, adding a default value of native architecture (the
same as if no --target argument is present).  Update the documentation
at the top of the file to make it mandatory.