These are the extensions that don't depend on any external libraries
that might not be present. That means that libc is okay, for exampl,
but libgtk is not.  Since there's no unusual dependency, there's no
reason not to build these in every time.

Code in this directory should also be mostly orthogonal.  Even if you
had the libraries, you likely wouldn't want to build in both postgres
and mysql support - they both do the same thing.  In the standard
extension, we only want one of each thing.




