pck-update: stricter checks on buildreqs with explicit arch

plugins/pck-update.in

@@ -1991,12 +1991,12 @@ build requirement found"": \`${NOTE}$f${NORM}' ""\
             # remove duplicates
             buildreqs_to_install=(
 $(for f in ${buildreqs_to_install[@]}; do
-   if [ "${f/.*}" != "${f}" ]; then
+   if [ "${f/*.}" == "arm" -o "${f/*.}" == "x86_64" -o "${f/*.}" == "i586" ]; then
       # if arch specified convert e.g. package.i586 to package@i586
       echo ${f/./@}
-   elif [ "${BUILD_ARCH}" == "x86_64" ]; then
+   elif [ "${BUILD_ARCH}" == "x86_64" -a "${target_cpu}" != "x86_64" ]; then
       # x86_64: specifying arch is necessary (FIXME: problems with .noarch)
-      echo $f@$target_cpu
+      echo $f@${target_cpu}
    else
       # classic behaviour
       echo $f