Fixes fig2dev build problem

Added a patch that solves https://github.com/mistydemeo/homebrew-xfig/issues/2

the function ends with ```return;```, which clang does not like if the function has not been explicitly declared as ```void```. gcc is less strict about this, this is why it has not been noticed before, I guess.
But fundamentally, this is a bug in xifg. I will try to report it to the developers.