toolchain: add support of ARC architecture

This includes binutils, gcc, gdb and uClibc-ng.

Latest release of ARC gcc (as of today it is "arc-2015.06")
is based on upstream gcc 4.8.4.

Sources are available on GitHub, see:
https://github.com/foss-for-synopsys-dwc-arc-processors/gcc

Latest release of ARC binutils (as of today it is "arc-2015.06")
is based on upstream binutils 2.23.

Sources are available on GitHub, see:
https://github.com/foss-for-synopsys-dwc-arc-processors/binutils-gdb/releases/tag/arc-2015.06

Latest release of ARC GDB (as of today this is "arc-2015.06-gdb")
is based on upstream gdb 7.9.1.

Sources are available on GitHub, see:
https://github.com/foss-for-synopsys-dwc-arc-processors/binutils-gdb/releases/tag/arc-2015.06-gdb



Note that for binutils and gdb that come from unified git repository
(which is the case for upstream binutils/gdb today) we need to disable
building of gdb in binutils and binutils in gdb hence in binutils:
------>8------
--disable-sim
--disable-gdb
------>8------

and in gdb:
------>8------
--disable-binutils
--disable-ld
--disable-gas
------>8------

Also in gdb we disable sim because if the following breakage while
building with it:
------------>8------------
/usr/bin/env bash ./../common/genmloop.sh -shell /usr/bin/env bash \
        -mono -fast -pbb -switch sem5-switch.c \
        -cpu a5f -infile ./mloop5.in \
        -outfile-suffix 5
unknown option: bash
Makefile:699: recipe for target 'stamp-5mloop' failed
make[7]: *** [stamp-5mloop] Error 1
------------>8------------

Cc: Felix Fietkau <nbd@openwrt.org>
Cc: John Crispin <blogic@openwrt.org>
Cc: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

SVN-Revision: 47438