Omissions from obligatory interfaces:
-------------------------------------
stdlib.h: _Exit, a64l, l64a, lcong48, lldiv, mkstemp, posix_openpt;
          mktemp, ecvt, fcvt
ndbm.h: [all=9] dbm_*
utmpx.h: [all=6] *utx* (but functions without "x" do exist!)
nl_types.h: [all] catclose, catgets, catopen
unistd.h: getwd, ualarm
inttypes.h: imaxdiv
fmtmsg.h: fmtmsg
string.h: strerror_r
setjmp.h: setsigjmp
monetary.h: strfmon
sys/select.h: pselect
sys/socket.h: sockatmark
sys/wait.h: waitid