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.

libroot/x86_64: minor improvements in TLS code

* less inline asm
* std::atomic<> instead of obsolete atomic_*()

runtime_loader: add support for ELF based TLS

This patch introduces support of ELF based TLS handling with lazy allocation
and initalization of TLS block for each DSO and thread. The implementation
generally follows the official ABI except that generation counter in dtv
is in fact a pointer to Generation object that contains both generation
counter and size of the dtv. That simplified the implementation a bit, but
could be changed later. The ABI requirements regariding in memory position
of TLS block is not honoured what results in static TLS model being
unsupported. However, that should not be a problem as long as
"executables" in Haiku are in fact shared objects and optimizations which
require specific TLS block in memory layout are not possible anyway.

libroot/x86[_64]: relax asm constraints in tls_*() functions

Implemented TLS for x86_64.

Added a dumb TLS implementation rather than printing an error.

Will properly implement TLS soon, for now a "working" implementation
is needed for anything to work properly.

Added some libroot bits for x86_64.

Still some parts missing (the glibc bits + fenv.c), plus the TLS
functions are only stubs.

libroot/x86_64: minor improvements in TLS code

* less inline asm
* std::atomic<> instead of obsolete atomic_*()

runtime_loader: add support for ELF based TLS

This patch introduces support of ELF based TLS handling with lazy allocation
and initalization of TLS block for each DSO and thread. The implementation
generally follows the official ABI except that generation counter in dtv
is in fact a pointer to Generation object that contains both generation
counter and size of the dtv. That simplified the implementation a bit, but
could be changed later. The ABI requirements regariding in memory position
of TLS block is not honoured what results in static TLS model being
unsupported. However, that should not be a problem as long as
"executables" in Haiku are in fact shared objects and optimizations which
require specific TLS block in memory layout are not possible anyway.

libroot/x86[_64]: relax asm constraints in tls_*() functions

Implemented TLS for x86_64.

Added a dumb TLS implementation rather than printing an error.

Will properly implement TLS soon, for now a "working" implementation
is needed for anything to work properly.

Added some libroot bits for x86_64.

Still some parts missing (the glibc bits + fenv.c), plus the TLS
functions are only stubs.