export isl_multi_*_zero
export isl_multi_*_zero

Now that isl_space has been exported, it becomes possible
to construct a zero-valued function from a space.
Since the space argument does not uniquely determine
which function should be constructed, this function
needs to be exported as a named constructor.

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl