AVX illegal instruction in job submitted from PyROOT

Note that, serious problems have been reported in this thread, when libraries built with and without “avx features” have been mixed:

@Axel So, the “cppyy backend” should be FORCED to use “avx features” if the ROOT itself was compiled with them (i.e., ROOT libraries). Otherwise, even if “avx” is present in the actual “/proc/cpuinfo”, they should NOT be used.