improve build script

rpmbuild/build.sh

@@ -4,7 +4,15 @@ set -Eeuo pipefail
 
 mkdir -p RPMS SRPMS BUILD BUILDROOT
 
-for spec in SPECS/*.spec; do
+if [ $# -gt 0 ]; then
+  for pkg; do
+    spectool -g -R SPECS/$pkg.spec
+    rpmbuild -ba SPECS/$pkg.spec
+  done
+else
+  for spec in SPECS/*.spec; do
     spectool -g -R $spec
     rpmbuild -ba $spec
-done
+  done
+fi
+