Log Message:
cad/librecad: Regularize and tweak language feature cleanup

  - rearrange the variables into canonical order and group all
    LANGUAGES stuff together.  NFCI
  - fix USE_LANGUAGES
  - read enough upstream makefiles to figure out that both c++11 and
    gnu++11 appear and where they from
  - remove -std=c++11 as well as gnu++11
  - require and force gnu++14, on the theory that it should be ok with
    both gnu++11 (librecad) and c++14 (boost)

Build tests and runs on on NetBSD 10 amd64, gcc 10.

(handed off to me for tweaking in private mail)