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>
gdb: bump to 7.7

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #442 from davidlt/gdb-7.7

gdb: bump to 7.7
Merge pull request #439 from davidlt/root5-linuxarm-cxx11

root: add support for C++11 mode for `linuxarm' target
Disabling Rivet2 dependency.

Rivet2 configuration does not work correctly on slc6, further investigation required.
Merge pull request #443 from degano/rivet2_disabled

Disabling Rivet2 dependency.
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable