spec: Improve the rpm package

This still needs a lot of work by a packaging specialist.

spec.in

@@ -12,11 +12,14 @@ Source0:	https://dl.fedoraproject.org/pub/alt/purpleidea/__PROGRAM__/SOURCES/__P
 # graphviz should really be a "suggests", since technically it's optional
 Requires: graphviz
 
-BuildRequires:	golang
+# If go_compiler is not set to 1, there is no virtual provide. Use golang instead.
+BuildRequires:  %{?go_compiler:compiler(go-compiler)}%{!?go_compiler:golang}
 BuildRequires:	golang-googlecode-tools-stringer
 BuildRequires:	git-core
 BuildRequires:	mercurial
 
+ExclusiveArch:  %{go_arches}
+
 %description
 A next generation config management prototype!