We used to build baremetal (AKA Elf32) multilibbed toolchains for years
now but never made that for Linux targets since there were problems with
uClibc n multilib setup. Now with help of Crosstool-NG it is finally
possible to create uClibc-based multilibbed toolchains and so we add
relevant CPUs for multilib in case of configuration for "arc*-*-linux*".

This will be essentially useful for glibc-based multilibbbed toolchains
in the future.

gcc/
2018-05-16  Alexey Brodkin <abrodkin@synopsys.com>

        * config.gcc: Add arc/t-multilib-linux to tmake_file for
        arc*-*-linux*.
        * config/arc/t-multilib-linux: Specify MULTILIB_OPTIONS and
        MULTILIB_DIRNAMES

From-SVN: r260434