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>
(transplanted from ec30b191f0e3fe9bc73199f0bcb8d789db17aa92)

# Menu for the native gdbserver

config GDB_GDBSERVER

    bool

    prompt "gdbserver"

    default n

    depends on ! BARE_METAL

    help

      Build and install a gdbserver for the target, to run on the target.

if GDB_GDBSERVER

config GDB_GDBSERVER_STATIC

    bool

    prompt "Build a static gdbserver"

    default y

    help

      In case you have trouble with dynamic loading of shared libraries,

      you will find that a static gdbserver comes in handy.

endif # GDB_GDBSERVER

if BARE_METAL

comment "In bare-metal, you'll need to   "

comment "provide your own gdbserver stub."

endif # BARE_METAL