Do not force to run atexit handlers, which text comes from a dso
owning the handle passed to __cxa_finalize() but which are registered
by other dso, when the process is inside exit(3).

Running them makes the destruction order wrong, and there is hope that
such destructors would not call dlclose(3), since it is pointless at
this stage of the process existence.

The change effectively disables the r211706 after the exit(3) is
called.

Reported and tested by:	Michael Gmelin <freebsd@grem.de>
Analyzed by:	dim
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Build an allocator for the aligned memory on top of the rtld-private
malloc.

Reviewed by:	kan
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
For variant II static TLS, properly align tls segments.  Pre-calculate
the max required alignment for the static tls segments, and honor it
when carving the pieces for next module, from the static space.  Use
aligned allocator to get properly-aligned dynamic blocks.

Reported by:	dt71@gmx.com
Reviewed by:	kan
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Disallow optimizations which potentially remove boundary checks
for signed values due to a compiler authors considering integer
overflow as impossible.

The change follows suit of other projects taking the same measure.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week