support/config-fragments/autobuild: add ARC glibc fragment

glibc is now supported for ARC so let's kick-start autobuilders
with glibc toolchain for ARC HS.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>