runtime_loader: define _LOADER_MODE for arch directories

Change-Id: I7eb6b77502eed76a529657d9ec733b72c9fc89c0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3275
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

runtime_loader: add hybrid support.

kernel, libroot: use C++11 atomics in atomic_*()

The less assembler in our sources the better. These functions wouldn't
be used very much since SupportDef.h inlines them, but the symbols should
be available.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>

More work towards hybrid support

* All packaging architecture dependent variables do now have a
respective suffix and are set up for each configured packaging
architecture, save for the kernel and boot loader variables, which
are still only set up for the primary architecture.
For convenience TARGET_PACKAGING_ARCH, TARGET_ARCH, TARGET_LIBSUPC++,
and TARGET_LIBSTDC++ are set to the respective values for the primary
packaging architecture by default.
* Introduce a set of MultiArch* rules to help with building targets for
multiple packaging architectures. Generally the respective targets are
(additionally) gristed with the packaging architecture. For libraries
the additional grist is usually omitted for the primary architecture
(e.g. libroot.so and <x86>libroot.so for x86_gcc2/x86 hybrid), so that
Jamfiles for targets built only for the primary architecture don't
need to be changed.
* Add multi-arch build support for all targets needed for the stage 1
cross devel package as well as for libbe (untested).

Support x86_64 in the runtime loader.

* Added x86_64 linker script and relocation code.
* Some 64-bit safety fixes to the heap code.
* Added runtime_loader, libroot and bash to the x86_64 image. The boot
script will be launched, but will panic shortly after because fork
is broken.

kernel, libroot: use C++11 atomics in atomic_*()

The less assembler in our sources the better. These functions wouldn't
be used very much since SupportDef.h inlines them, but the symbols should
be available.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>

More work towards hybrid support

* All packaging architecture dependent variables do now have a
respective suffix and are set up for each configured packaging
architecture, save for the kernel and boot loader variables, which
are still only set up for the primary architecture.
For convenience TARGET_PACKAGING_ARCH, TARGET_ARCH, TARGET_LIBSUPC++,
and TARGET_LIBSTDC++ are set to the respective values for the primary
packaging architecture by default.
* Introduce a set of MultiArch* rules to help with building targets for
multiple packaging architectures. Generally the respective targets are
(additionally) gristed with the packaging architecture. For libraries
the additional grist is usually omitted for the primary architecture
(e.g. libroot.so and <x86>libroot.so for x86_gcc2/x86 hybrid), so that
Jamfiles for targets built only for the primary architecture don't
need to be changed.
* Add multi-arch build support for all targets needed for the stage 1
cross devel package as well as for libbe (untested).

Support x86_64 in the runtime loader.

* Added x86_64 linker script and relocation code.
* Some 64-bit safety fixes to the heap code.
* Added runtime_loader, libroot and bash to the x86_64 image. The boot
script will be launched, but will panic shortly after because fork
is broken.