Be *stupider* about what constitutes a supported language binding.

We were trying to be super smart and find all the supported language
bindings.  This led to us scanning the directory and treating all
subdirectories as language binding directories.  This makes it
hard to add unrelated code in this folder.

Besides, we only support one at the moment - Python.  And when new
ones are added it will be trivial to just add their names to a list.

So this patch gets stupider about how to look for language binding
subfolders.  Just put them in a list, and use the list.

llvm-svn: 254078