Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r232582 (partial)

- Switch ARM to TLS Variant I.
- Fix TLS allocation for Variant I: both rtld and libc allocators
assume that tls_static_space includes space for TLS structure.
So increment calculated static size by the size of it.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

The static TLS size as given by tls_static_space includes TLS_TCB_SIZE
bytes of TCB in variant I.

o Add MIPS to the list of architectures with defined TLS_TCB_ALIGN
o Stick with TLS Variant II for MIPS for the moment.

Approved by: imp

Don't assert() the TLS allocation requested is big enough; just
fix the argument.

In particular, this is a step towards breaking crt1's dependence on stdio.

Fix TLS on sparc64 for statically and dynamically linked binaries
Approved by: rwatson (mentor)
Reviewed by: jmg and marcel

Fix style(9) in code copied from rtld.

Fix the variant I allocation for KSE: Allow a larger TCB and assume
that the documented TCB is at the tail of the extended TCB. In other
words, the base of the TCB has a negative offset from the TLS.

Remove stale comment about arm

Allocate space for thread pointer, this allows thread library to access
its pointer from begin, and simplifies _get_curthread() in libthr.

Use __weak_reference macro to define weak symbols.

Fix incorrect comment.

Mark _rtld_allocate_tls and _rtld_free_tls as weak symbols for Variant I
tls.

Reviewed by: dfr

Arbitraly choose the Variant II for arm.

Make sure we allocate at least enough space for the TCB for variant I TLS.

MFC after: 3 days

Always allocate a TLS area even if its empty - libpthread relies on
having a valid %gs when it initialises.

MFC after: 2 days

Add support for TLS in statically linked programs.

Add stubs for TLS functions. These will be replaced at runtime by the
functional versions in rtld.