simplify BuildRequires

packaging/redhat/zeromq.spec

@@ -67,19 +67,17 @@ BuildRequires:  gnutls-devel
 %else
 %define TLS no
 %endif
-
-
-%if 0%{?suse_version}
-BuildRequires:  rubygem(asciidoctor)
-%else
-%if 0%{?rhel_version} || 0%{?rhel} || 0%{?centos_version} 
-BuildRequires:  rubygem-asciidoctor
-%else
+%if 0%{?rhel_version}
+%if 0%{?rhel_version} > 700
+# note1: on OBS the RHEL7 target for some reason is unable to find the asciidoctor package, so on RHEL7 docs are not built
+# note2: on RHEL8/Centos8 the asciidoctor package depends from the ruby module; this might require some extra config on the
+#        build farm where this .spec file is used
 BuildRequires:  asciidoctor
 %endif
+%else
+# on non-RHEL targets, listing asciidoctor in BuildRequires works just fine:
+BuildRequires:  asciidoctor
 %endif
-
-
 BuildRequires: gcc, make, gcc-c++, libstdc++-devel
 Requires:      libstdc++