Description of Problem:

Function 'rpm-build' instead of using start-process should really set
'compilation-command' variable and run 'compile'.  The real difference is how you
are walking through errors in a compilation buffer as opposed to "Fundamental"
one.  Run "M-x compile" and replace a default compilation commmand by
something like "rpmbuild -ba my.spec" to see for yourself.

This will also likely simplify rpm-spec-mode.el a small bit.