The tcpick package relies heavily on implicit function declarations:

conftest.c:29: implicit function declaration: exit                              
timer.c:111: implicit function declaration: status_switch                       
loop.c:106: implicit function declaration: out_flavour
verify.c:115: implicit function declaration: flush_ack                          verify.c:139: implicit function declaration: newconn
verify.c:170: implicit function declaration: status_switch               
timer.c:90: implicit function declaration: signal_setup
loop.c:101: implicit function declaration: verify                               timer.c:82: implicit function declaration: err                                  loop.c:98: implicit function declaration: display_header                        timer.c:81: implicit function declaration: sorry                                loop.c:50: implicit function declaration: fault                                 write.c:68: implicit function declaration: fault                                write.c:198: implicit function declaration: out_flavour                         write.c:266: implicit function declaration: out_h                               write.c:269: implicit function declaration: out_hn                              quit.c:39: implicit function declaration: err                                   write.c:86: implicit function declaration: getportname          
write.c:263: implicit function declaration: out_p
write.c:252: implicit function declaration: out_xa                              write.c:255: implicit function declaration: out_x
fragments.c:174: implicit function declaration: flowflush
write.c:245: implicit function declaration: color
quit.c:41: implicit function declaration: color
datalink.c:221: implicit function declaration: suicide
tracker.c:102: implicit function declaration: free_desc
tcpick.c:206: implicit function declaration: err
tcpick.c:169: implicit function declaration: suicide
tcpick.c:254: implicit function declaration: datalink2off
display.c:96: implicit function declaration: time_ascii
lookup_query.c:42: implicit function declaration: _l_insert
tcpick.c:130: implicit function declaration: msg
tcpick.c:96: implicit function declaration: set_timer
tcpick.c:126: implicit function declaration: fault
tcpick.c:82: implicit function declaration: sorry
tcpick.c:93: implicit function declaration: parse_args
verify.c:106: implicit function declaration: addfr
args.c:54: implicit function declaration: color
display.c:111: implicit function declaration: getportname
display.c:248: implicit function declaration: isgraph
tracker.c:38: implicit function declaration: display_status
tracker.c:42: implicit function declaration: rmconn
display.c:97: implicit function declaration: color
display.c:198: implicit function declaration: iscntrl
display.c:198: implicit function declaration: isascii
args.c:216: implicit function declaration: suicide
args.c:105: implicit function declaration: err
loop.c:45: implicit function declaration: check_expired
quit.c:74: implicit function declaration: msg

… and more. We need to build it in C89 mode because implicit function declarations were removed from C99.

Reproducible: Always