rpm: Require redhat-rpm-config at run time for el8

Starting with el8 annobin is used to annotate ELF binaries and this is
set up via the %configure RPM macro. As a result annobin becomes a
requirement of the default cc_command in varnishd but it relies on GCC
spec files that are provided by redhat-rpm-config.

So, similar to how we explicitly require GCC at run time we now also
need to bring the annobin setup.

redhat/varnish.spec

@@ -23,6 +23,9 @@ BuildRequires: python3-sphinx
 Requires: gcc
 Requires: logrotate
 %systemd_requires
+%if 0%{?rhel} >= 8
+Requires: redhat-rpm-config
+%endif
 
 Provides:  varnish-libs%{?_isa} = %{version}-%{release}
 Provides:  varnish-libs = %{version}-%{release}