libroot/arch/arm: use TLS for getting current thread ID

Change-Id: I424f4029f29a362af9b1ea814b518d59aeae271d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5541
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: David Karoly <karolyd577@gmail.com>

libroot: Some fixes for Clang ARM builds.

ARM: Break apart ARMv5 and older dsb/dmb

* Add isb just because.
* pdziepak pointed out that ARMv5 and before
had different barrier support.
* pdziepak also mentioned that dsb was too strong
for __sync_synchronize

ARM: Add ARMv6 or older __sync_synchronize built-in

* On ARMv6 or older, we do a simulated dsb.
* Move __sync_synchronize into thread.c in libroot
and use the new arch_atomic.h dsb/dmb defines.
* Gets arm @bootstrap-raw to end of bootstrap.

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

ARM: Break apart ARMv5 and older dsb/dmb

* Add isb just because.
* pdziepak pointed out that ARMv5 and before
had different barrier support.
* pdziepak also mentioned that dsb was too strong
for __sync_synchronize

ARM: Add ARMv6 or older __sync_synchronize built-in

* On ARMv6 or older, we do a simulated dsb.
* Move __sync_synchronize into thread.c in libroot
and use the new arch_atomic.h dsb/dmb defines.
* Gets arm @bootstrap-raw to end of bootstrap.

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