Switch to lowopt=True for libxc-2.2.* with intel compilers

I've noticed that some functionals in LibXC give significantly different
results with too much compiler optimization. For example, the energy of
a water molecule computed with the TPSS functional changes by 6.5 kJ/mol
with lowopt=False. (The problem is in the TPSS correlation functional,
somewhere in mgga_c_pkzb.c. I've ruled out numerical integration issues.
Similar relative errors appear on every grid point of the tpss_c energy
density.)

I can only test with libx-2.2.* and intel compilers at the moment. I'll
make similar changes for other versions and compilers when the
opportunity arises.