Check if getpeereid is actually declared.

Check in sys/socket.h (AIX) and unistd.h (FreeBSD, DragonFLy and OS X).
Prevents undeclared function warning on at least some versions of AIX.

configure.ac

@@ -1986,10 +1986,11 @@ AC_CHECK_DECL([tcsendbreak],
 
 AC_CHECK_DECLS([h_errno], , ,[#include <netdb.h>])
 
-AC_CHECK_DECLS([SHUT_RD], , ,
+AC_CHECK_DECLS([SHUT_RD, getpeereid], , ,
 	[
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <unistd.h>
 	])
 
 AC_CHECK_DECLS([O_NONBLOCK], , ,

openbsd-compat/openbsd-compat.h

@@ -197,7 +197,7 @@ int writev(int, struct iovec *, int);
 #include "bsd-waitpid.h"
 #include "bsd-poll.h"
 
-#ifndef HAVE_GETPEEREID
+#if defined(HAVE_DECL_GETPEEREID) && HAVE_DECL_GETPEEREID == 0
 int getpeereid(int , uid_t *, gid_t *);
 #endif