modbuild: test for bash 5 or later, otherwise abort

Pmodules/modbuild.in

@@ -34,6 +34,14 @@ source libstd.bash    || {
         echo "Oops: cannot source library -- '$_'" 1>&2; exit 3;
 }
 
+if (( ${BASH_VERSINFO[0]} < 5 )); then
+	std::info "bash >= 5 is required! You are running bash ${BASH_VERSION} ..."
+	std::info "Make sure that bash >= 5 is in your PATH."
+	std::info "bash >= 5 is available as Pmodule:"
+	std::info "  module load System:bash"
+	std::die 3 ""
+fi
+
 std::def_cmds "${path}" \
 	      'awk' 'base64' 'find' 'getopt' 'logger' 'mktemp' \
 	      'rm' 'sort' 'find' 'yq'