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 cross GDB

config STATIC_TOOLCHAIN

    select GDB_CROSS_STATIC if GDB_CROSS

config GDB_CROSS

    bool

    prompt "Cross-gdb"

    default y

    select GDB_GDBSERVER if ! BARE_METAL

    help

      Build and install a cross-gdb for the target, to run on host.

if GDB_CROSS

config GDB_CROSS_STATIC

    bool

    prompt "Build a static cross gdb"

    default n

    help

      A static cross gdb can be usefull if you debug on a machine that is

      not the one that is used to compile the toolchain.

      That way, you can share the cross-gdb without installing a toolchain

      on every machine that will be used to debug target programs.

endif # GDB_CROSS