Setup IBs for CMSSW_7_4_CLANG_X

in cmssw:

I created branch CMSSW_7_4_CLANG_X from CMSSW_7_3_CLANG_X

https://github.com/cms-sw/cmssw/compare/CMSSW_7_3_CLANG_X...CMSSW_7_4_CLANG_X

The automatic merges should merge everything from CMSSW_7_4_X into CMSSW_7_4_CLANG_X

in cmsdist:

CMSSW_7_4_CLANG_X uses IB/CMSSW_7_4_X/stable