'The fortran and C/C++ versions of the XL compiler are always
two units apart.  By this we mean that the fortran release that
goes with XL C/C++ 11.1 is 13.1.  Having such a difference in
version number is confusing spack quite a lot.  Most notably
if you keep the versions as is the default xl compiler will
only have fortran and no C/C++.  So we associate the Fortran
compiler with the version associated to the C/C++ compiler.
One last stumble. Version numbers over 10 have at least a .1
those under 10 a .0. There is no xlf 9.x or under currently
available. BG/P and BG/L can such a compiler mix and possibly
older version of AIX and linux on power.'

@classmethod
def fc_version(cls, fc):

    fver = get_compiler_version(fc, '-qversion', '([0-9]?[0-9]\\.[0-9])')
    cver = (float(fver) - 2)
    if (cver < 10):
        cver = (cver - 0.1)
    return str(cver)
