"Conflicting types" build failure(s) — clang 12.0.1

clang considers conflicting declarations as error while gcc just shows a warning
// clang  -c  foo.c
#include <stdio.h>
char *getline(int fd) { return NULL; }
PackageVersionSupposed error messageFull log Bug report
dcl 7.4.1-1cmsgdmp.c:210:27: error: conflicting types for 's_copy' Log
freefem 3.5.8-7setjmp.h:54:12: error: conflicting types for '__sigsetjmp' Log
k2pdfopt 2.53+ds-1ocrtess.c:300:6: error: conflicting types for 'ocrtess_baselang' Log
opensmtpd-extras 6.7.1-2stdio.h:354:12: error: conflicting types for 'snprintf' Log
pccts 1.33MR33-6genmk.c:971:1: error: conflicting types for 'pclasses' Log 753538

5 errors