libsys: don't try to expose freebsd7___semctl

This has always been in libc and never exported directly. I accidently
included it along side some freebsd11_* symbols based on a tree where I
moved semctl(2).

Fixes: df1a09ba524d0 libsys: expose a few more symbols for libc's use

Make __libsys_interposing_slot libsys only

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D44881

libsys: expose a few more symbols for libc's use

These private symbols are used by libc so expose as we do with
auxargs bits rather then relying on duplicate implementations in libc.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D44114

libsys: don't expose __init_elf_aux_vector

__init_elf_aux_vector is now complied statically so don't try to export
it from the dynamic library.

Fixes: 8271d9b99a3b libsys: remove usage of pthread_once and _once_stub

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D44237

lib{c,sys}: move auxargs more firmly into libsys

Continue to filter the public interface (elf_aux_info()), but entierly
relocate the private interfaces (_elf_aux_info(),
__init_elf_aux_vector(), and __elf_aux_vector) to libsys.

This ensures that rtld updates the correct (only) copy of
__elf_aux_vector. After 968a18975adc9c2a619bb52aa2f009de99fc9e24
updates were confused and __getosreldate was failing, causing
the system to fall back to compat compat12 syscalls in some cases.

Return to explicitly linking libc to libsys and link libthr with libc
and libsys (in that order).

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D43910