libroot: Compile x86_64's arch_string with -fno-builtin.

Otherwise, GCC and Clang create infinite recursions.
Fixes #15827.

kernel,libroot,boot: remove c++11 and gnu++11 flags.

* c++14 is the default with current GCC
* remove pragmas for x86intrin.h

kernel/x86_64: remove memset and memcpy from commpage

There is absolutely no reason for these functions to be in commpage,
they don't do anything that involves the kernel in any way.

Additionaly, this patch rewrites memset and memcpy to C++, current
implementation is quite simple (though it may perform surprisingly
well when dealing with large buffers on cpus with ermsb). Better
versions are coming soon.

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).

Added some libroot bits for x86_64.

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

kernel/x86_64: remove memset and memcpy from commpage

There is absolutely no reason for these functions to be in commpage,
they don't do anything that involves the kernel in any way.

Additionaly, this patch rewrites memset and memcpy to C++, current
implementation is quite simple (though it may perform surprisingly
well when dealing with large buffers on cpus with ermsb). Better
versions are coming soon.

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).

Added some libroot bits for x86_64.

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