After running ./configure && make on AIX:
assuan-socket-server.c: In function 'accept_connection_bottom': assuan-socket-server.c:134:9: warning: implicit declaration of function 'getpeereid'; did you mean 'getpgid'? [-Wimplicit-function-declaration] 134 | if (getpeereid (fd, &ctx->peercred.uid, &ctx->peercred.gid) != -1) | ^~~~~~~~~~ | getpgid
This platform needs _ALL_SOURCE defined for this function.