ARC: update tools to arc-2015.06 release

I'm happy to update GNU tools for ARC cores to the most recent
arc-2015.06 release.

This release brings following major improvements:
 * GCC: source update to v4.8.4
 * GCC: C ABI compatibility between MetaWare and GNU toolchains
 * uClibc: support for thread local storage and Native Pthread Library (NPTL)
 * GDB: updated to version 7.9.1

Also a lot of fixes and improvements has been done, please refer to
https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/releases/tag/arc-2015.06


for more details.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Anton Kolesov <akolesov@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>