root: add support for C++11 mode for `linuxarm' target

Add missing fragments to `linuxarm' target Makefile to support C++11
mode.

Cleanup unneeded parts in SPEC.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge pull request #439 from davidlt/root5-linuxarm-cxx11

root: add support for C++11 mode for `linuxarm' target