refactor: separate undocumented compat APIs.

* lib/posix/compat.lua (doselection, PosixTm, LegacyTm, pushmode)
(bind, clock_getres, clock_gettime, connect, fadvise, fnmatch)
(getgroup, getpasswd, getpid, getrimit, gettimeofday, gmtime)
(hostid, isgraph, isprint, localtime, mktime, nanosleep, pathconf)
(setrlimit, stat, statvfs, strftime, strptime, sysconf, times)
(uname): Move from here...
* lib/posix/deprecated.lua (doselection, PosixTm, LegacyTm)
(pushmode, bind, clock_getres, clock_gettime, connect, fadvise)
(fnmatch, getgroup, getpasswd, getpid, getrimit, gettimeofday)
(gmtime, hostid, isgraph, isprint, localtime, mktime, nanosleep)
(pathconf, setrlimit, stat, statvfs, strftime, strptime, sysconf)
(times, uname): New file.  ...to here.
* build-aux/sanity-cfg.mk (sc_error_message_uppercase): Adjust
accordingly.
* build-aux/config.ld.in (file): Add lib/posix/compat.lua.
* lib/posix/compat.lua: Document within posix module.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>