complibs/ppl: build only C and C++ interfaces for PPL
By default, PPL wants to build interfaces for any of a variety of
langauges it finds on the local host (python, java, possibly perl, also
more esoteric languages such as ocaml and prolog).
These extra interfaces can double the compile time for the library. For
single-process builds, I found a savings of more than 40%:
default / j1: 716s total, 143.2s avg, 0.52s stdev
just_c / j1: 406s total, 81.2s avg, 0.33s stdev
just_c_cpp / j1: 413s total, 82.6s avg, 0.22s stdev
And for multi-process builds, it approached 50%:
default / j4: 625s total, 125.0s avg, 0.57s stdev
just_c / j4: 338s total, 67.6s avg, 1.25s stdev
just_c_cpp / j4: 327s total, 65.4s avg, 0.36s stdev
Since the PPL we build within ct-ng is only used by GCC, we only need to
build the C and C++ interfaces.
Signed-Off-By: Anthony Foiani <anthony.foiani@gmail.com>