I don’t have a solution, but you may try the following … recreate the “source tree” from scratch (so that no old building remnants are present) and then use a “build tree” which is separate from the “source tree” (do not build ROOT 6 “in place”) and use cmake (do not use “configure + make” for ROOT 6): cd /Where/You/Build/It
unset ROOTSYS
cmake -Dall="ON" -Dsoversion="ON" /Where/The/Source/Code/Is > cmake.out.txt 2>&1
cmake --build . >> cmake.out.txt