fix for insidious bug that skips function declarations in an extern C context if their name does not contain an _ in the last position.
Merge pull request #5592 from gartung/clangSA-fix-function-checker-externcfunc

fix for insidious bug that skips function declarations in an extern C
Merge remote branch 'origin/CMSSW_7_2_X' into CMSSW_7_0_X