Compile warnings

[xavierba]

Current maint branch with #36 applied still generate a couple compile warning:

./send_nsca.c: In function 'alarm_handler':
./send_nsca.c:543:2: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
  543 |  write(STDOUT_FILENO, msg, sizeof(msg) - 1);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./nsca.c: In function 'main':
./nsca.c:159:3: warning: ignoring return value of 'getcwd', declared with attribute warn_unused_result [-Wunused-result]
  159 |   getcwd(config_file,sizeof(config_file));
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./nsca.c: In function 'write_checkresult_file':
./nsca.c:1285:9: warning: ignoring return value of 'asprintf', declared with attribute warn_unused_result [-Wunused-result]
 1285 |         asprintf(&checkresult_file,"%s/cXXXXXX",check_result_path);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./nsca.c:1319:9: warning: ignoring return value of 'asprintf', declared with attribute warn_unused_result [-Wunused-result]
 1319 |         asprintf(&checkresult_ok_file,"%s.ok",checkresult_file);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./nsca.c: In function 'write_pid_file':
./nsca.c:1508:3: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
 1508 |   write(fd,pbuf,strlen(pbuf));
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
./nsca.c:1509:3: warning: ignoring return value of 'fchown', declared with attribute warn_unused_result [-Wunused-result]
 1509 |   fchown(fd,usr,grp);
      |   ^~~~~~~~~~~~~~~~~~
./nsca.c: In function 'find_rhand':
./nsca.c:743:9: warning: control reaches end of non-void function [-Wreturn-type]
  743 |         }
      |         ^
./nsca.c: In function 'find_whand':
./nsca.c:759:9: warning: control reaches end of non-void function [-Wreturn-type]
  759 |         }
      |         ^
./nsca.c: In function 'read_config_file':
./nsca.c:495:29: warning: ignoring return value of 'asprintf', declared with attribute warn_unused_result [-Wunused-result]
  495 |                             asprintf(&checkresult_test,"%s/nsca.test.%i",check_result_path,getpid());
      |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~