[Buildroot] gst-plugins-base alsa dependency

[Phil Edworthy]

> > How can a Buildroot package be told of build order dependencies,
> > without requiring the packages to be included?
> 
> By doing something like:
> 
> ifeq ($(BR2_PACKAGE_ON_WHICH_I_DEPEND),y)
> MYPKG_DEPENDENCIES += package-on-which-i-depend
> endif
> 
> If the package "package-on-which-i-depend" is enabled in the
> configuration, then you will have the guarantee that it gets compiled
> before the current package.

Thanks Thomas, that's a nice and simple way to fix it.
Phil