config: move DEBUG IB to GCC 4.9.0 and IB/CMSSW_7_1_X/debug branch

The new branch relies on GCC 4.9.0 and provides optimized and compressed
debug information.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge pull request #608 from davidlt/config-debug-ib

config: move DEBUG IB to GCC 4.9.0 and IB/CMSSW_7_1_X/debug branch