TLS.h: Drop inline assembly from the header.

This was a holdover from BeOS, which did this as inline assembly.
We do not on any platform other than 32-bit x86, and even there
we may have preferred to do things a little differently on non-BeOS
ABIs.

Most things ported from other systems, or even native apps, are going to
use _Thread_local variables anyway, which will bypass this system
altogether.

sparc: add defines and minimum set of required files

Gets the stage0 bootstrap to run.
Imlementation is probably nonsense at this point.

Change-Id: I10876efbb54314b864c0ad951152757cdb2fd366
Reviewed-on: https://review.haiku-os.org/c/1061
Reviewed-by: waddlesplash <waddlesplash@gmail.com>