# Join two lists with a comma if necessary.
m4_define([b4_list2],
[$1[]m4_ifval(m4_quote($1), [m4_ifval(m4_quote($2), [[, ]])])[]$2])
# Join two lists with a comma if necessary.
m4_define([b4_list2],
[$1[]m4_ifval(m4_quote($1), [m4_ifval(m4_quote($2), [[, ]])])[]$2])