get .c filename from atom

Still a problem for riak_error:
/tmp/__eqc_tmp1380720478577526_riak_error_iface.erl:23: Warning: function check_types/2 is unused
Undefined symbols for architecture x86_64:
  "_errmsgs", referenced from:
      ___eqc_c_address_of_errmsgs in ccRnjEeV.o
     (maybe you meant: ___eqc_c_address_of_errmsgs)
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status