Do not assume that mode_t uses the

Do not assume that mode_t uses the
traditional octal encoding.  E.g. "chmod 1 FOO" should set
the other-execute bit of FOO even if S_IXOTH != 1.

(SUID, SGID, SVTX, RUSR, WUSR, XUSR, RGRP, WGRP, XGRP, ROTH,
WOTH, XOTH, ALLM): New macros.
(S_ISUID, S_ISGID, S_ISVTX, S_IRUSR, S_IWUSR, S_IXUSR,
 S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH, S_IXOTH):
Use them.
(S_ISGID): Fix typo; it was defaulting to the same value as S_ISUID.
(S_IRWXU, S_IRWXG, S_IRWXO): Specify defaults in terms of the above.
(mode_compile):
No need to use uintmax_t; unsigned long is long enough.
Don't bother to get suffix since we don't use it.