relaxng: add 'arch' attr for <group/category/environment>

I assume it has the same meaning as for <packagereq> where it was
allowed previously.

comps.rng

@@ -43,6 +43,9 @@
     <element name="group">
       <!-- Example documentation. Please add more. -->
       <a:documentation>This defines a package group.</a:documentation>
+      <optional>
+        <ref name="arch"/>
+      </optional>
       <optional>
         <ref name="variant"/>
       </optional>
@@ -147,9 +150,7 @@
         </attribute>
       </optional>
       <optional>
-        <attribute name="arch">
-          <ref name="string"/>
-        </attribute>
+        <ref name="arch"/>
       </optional>
       <optional>
         <ref name="variant"/>
@@ -159,6 +160,9 @@
   </define>
   <define name="environment">
     <element name="environment">
+      <optional>
+        <ref name="arch"/>
+      </optional>
       <optional>
         <ref name="variant"/>
       </optional>
@@ -178,6 +182,9 @@
   </define>
   <define name="category">
     <element name="category">
+      <optional>
+        <ref name="arch"/>
+      </optional>
       <optional>
         <ref name="variant"/>
       </optional>
@@ -344,6 +351,11 @@
       </zeroOrMore>
     </element>
   </define>
+  <define name="arch">
+    <attribute name="arch">
+      <ref name="string"/>
+    </attribute>
+  </define>
   <define name="variant">
     <attribute name="variant">
       <data type="string"/>