'Checks if incompatible variants have been activated at the same time
:param spec: spec of the package
:raises RuntimeError: in case of inconsistencies'

def validate(self, spec):

    if (('+fortran' in spec) and (not self.compiler.fc)):
        msg = 'cannot    build    a    fortran    variant    without    a    fortran    compiler'
        raise RuntimeError(msg)
