[CMSSW_7_0_X][48] Update for GCC, fixes for Darwin platform, dead sources clean up, data packages update

**ChangeLog**
- Final changes for GCC 4.8.
- Fixes for Darwin platform (tested on _macms09_).
- Clean up dead sources.
- Build data packages by download files directly instead of looking into _download.url_ files in CMSSW packages.