Fix #149: unset CPPCHECK_EXECUTABLE correctly
Fix #149: unset CPPCHECK_EXECUTABLE correctly

ptoharia/CMake,ptoharia/CMake,biddisco/CMake,ptoharia/CMake,jafyvilla/CMake,shuaibarshad/KAUST-CMake,biddisco/CMake,biddisco/CMake,jafyvilla/CMake,shurikasa/CMake,shurikasa/CMake,shuaibarshad/KAUST-CMake,jafyvilla/CMake,shurikasa/CMake,shuaibarshad/KAUST-CMake,biddisco/CMake,shurikasa/CMake,jafyvilla/CMake,shuaibarshad/KAUST-CMake,ptoharia/CMake