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.

implement TLS for arm

Use the User Read-only Thread ID Register aka TPIDRURO to store
TLS pointer.

The User Read-only Thread ID Register is read-only in User mode,
and read/write in privileged modes.

see: ARMv7 Architecture Reference Manual,
section B3.12.46 CP15 c13 Software Thread ID registers

Change-Id: I7bff2fd66f41d7bf1a8a247151bcd02b32733c1b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4994
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>

s/OpenBeOS License/MIT License/ universally, as they're the same thing.

Fixes #8681.

arm: added some missing arch bits and changed asm section for arm compat.

arm: added some missing arch bits and changed asm section for arm compat.