Consider always running prototypes.py as part of make

(See WT-7114, where we needed to back out a change to run prototypes).

For this ticket, let's consider running the dist/prototypes.py script every time we run make.  That will keep src/include/extern.h up to date always, which is convenient for development.  The issue with doing this is that it requires (probably for the first time) that python be available as as requirement to build WiredTiger, even if you don't need the python interface (and didn't specify --enable-python).