Build the nonxs extensions before running mkppport.

Build the nonxs extensions before running mkppport.

(It requires several modules that we'd like to move from lib/ to ext/
In turn, as it runs before the dynamic extensions are built, it means that
all modules *they* require at configure and build time will already be in lib,
which simplifies things considerably. We then only need to worry about a
subset of pure-perl modules in ext/ that require each other to build.)