A forced commit to note other portion of the Makefile change accidentally

A forced commit to note other portion of the Makefile change accidentally
committed in r313972

The code committed in r313962 implicitly relies on python 2.x to generate
testvect.h . There are a handful of issues with this approach:

- python is not an explicit build dependency for FreeBSD
- python 2.x is deprecated and will be removed sometime in the future
  (potentially before 11.x's EOL), and the script does not function with
  python 3.5 (it uses deprecated idioms and incompatible function calls).
- python(1) (by default) lives in /usr/local/bin (${LOCALBASE}/bin) and
  gentestvect.py is a dependency of testvect.h (prior to r313972) which
  means that if the mtime of the generator script was newer than the
  mtime of the test vector, it could cause a spurious build failure in
  build time or at install time.

A better solution using C/C++ should be devised.

Discussed with:	allanjude
MFC after:	2 weeks
X-MFC with:	r313962, r313972
Sponsored by:	Dell EMC Isilon