erlang: disable parallel building

This fixes build errors like

 GEN    asn1ct_eval_ext.erl
{"init terminating in do_boot",{undef,[{asn1ct_func,start_link,[],[]},{prepare_templates,gen_asn1ct_eval,1,[{file,"prepare_templates.erl"},{line,58}]},{init,start_em,1,[]},{init,do_boot,3,[]}]}}
init terminating in do_boot ({undef,[{asn1ct_func,start_link,[],[]},{prepare_templates,gen_asn1ct_eval,1,[{_},{_}]},{init,start_em,1,[]},{init,do_boot,3,[]}]})

that occur on some machines but not others.