redundant = both left and right-hand side are in one of (C89/C99/POSIX), so I simply declare the old one to be redundant since the new one can cover the old's use case.

Obsolete Replacement Reason for using new
asctime strftime redundant
atof strtod error checking
atoi strtol error checking
atol strtol error checking
atoll strtoll error checking
atoq strtoll error checking, POSIX
bcmp memcmp POSIX
bcopy memcpy POSIX
brk mmap smarter, POSIX
bzero memset POSIX
ctime strftime redundant
ecvt snprintf POSIX
endutent endutxent POSIX
fcvt snprintf POSIX
futimes futimens high-resolution, POSIX
futimesat utimensat high-resolution, POSIX
gcvt snprintf POSIX
gethostbyaddr getaddrinfo/getnameinfo thread-safe, POSIX
gethostbyname getaddrinfo thread-safe, POSIX
getitimer timer_gettime high-resolution, POSIX
getprotobynumber getaddrinfo/getnameinfo? thread-safe, POSIX
getprotoent getaddrinfo thread-safe, POSIX
getpw getpwent redundant
gets fgets overflow-safer
getservbyname getaddrinfo thread-safe, POSIX
getservbyport getaddrinfo/getnameinfo thread-safe, POSIX
gettimeofday clock_gettime high-resolution, POSIX
getutent getutxent POSIX
getutid getutxid POSIX
getutline getutxline POSIX
getwd getcwd overflow-safe
inet_addr inet_pton thread-safe, multi-protocol, POSIX
inet_aton inet_pton thread-safe, multi-protocol, POSIX
inet_ntoa inet_ntop thread-safe, multi-protocol, POSIX
isascii isalpha/isdigit/etc. portable
itoa snprintf thread-safe, portable
matherr fenv
memalign posix_memalign
mktemp mkstemp security
msgctl mq_unlink POSIX
msgget mq_open POSIX
msgrcv mq_receive POSIX
msgsnd mq_send POSIX
msleep nanosleep high-resolution
pause sigsuspend redundant
pselect ppoll high-resolution
pututline pututxline POSIX
qecvt snprintf POSIX
qfcvt snprintf POSIX
qgcvt snprintf POSIX
scalb scalbln redundant
select poll high-resolution
semctl sem_wait/sem_post
semget sem_open POSIX
semop sem_? POSIX
setitimer timer_settime high-resolution
settimeofday clock_settime high-resolution
setutent setutxent POSIX
shmat shm_open POSIX
shmctl shm_unlink POSIX
shmdt close POSIX
shmget shm_open POSIX
sigblock sigprocmask POSIX
siggetmask sigprocmask POSIX
siginterrupt sigaction POSIX
sigmask sigaddset POSIX
signal sigaction POSIX
sigsetmask sigprocmask POSIX
sigvec sigaction POSIX
sleep nanosleep high-resolution
strtok strsep/strtok_r thread-safe
tempnam mkstemp security, POSIX
timegm mktime+setenv POSIX
timelocal mktime POSIX
tmpfile mkstemp security
tmpnam mkstemp security, POSIX
ualarm timer_settime high-resolution, POSIX
ulimit getrlimit/setrlimit POSIX
usleep nanosleep high-resolution, POSIX
utime utimensat high-resolution, POSIX
utimes utimensat high-resolution, POSIX
valloc posix_memalign POSIX