.la archives are prohibited by most Linux distributions because they
clutter up the linker. They may get caught up as victims in scripts that
purge .la files. Besides, .la files don't matter for simple loadable
modules on most systems.
So, what we do now instead is just use the platform suffix detected by
libtool.
Due to reversed conditionals, it wasn't being generated properly.
This also actually fixes its generation in librb by just copying the
Charybdis version. Unbundlers will want to take note of this.
