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>

# Linux kernel options

if KERNEL_LINUX_INSTALL

choice

    bool

    prompt "Kernel verbosity:"

    default KERNEL_LINUX_VERBOSITY_0

config KERNEL_LINUX_VERBOSITY_0

    bool

    prompt "Simplified"

    help

      Print simplified command lines.

config KERNEL_LINUX_VERBOSITY_1

    bool

    prompt "Full commands"

    help

      Print full command lines.

config KERNEL_LINUX_VERBOSITY_2

    bool

    prompt "Exec reasons"

    help

      Print the reasons why a make target is rebuild.

endchoice

config KERNEL_LINUX_VERBOSE_LEVEL

    int

    default 0 if KERNEL_LINUX_VERBOSITY_0

    default 1 if KERNEL_LINUX_VERBOSITY_1

    default 2 if KERNEL_LINUX_VERBOSITY_2

config KERNEL_LINUX_INSTALL_CHECK

    bool

    prompt "Check installed headers"

    default y

    help

      If you are in doubt that installed headers are buggy, say 'Y'

      here to have an extra check passed onto the headers.

endif # KERNEL_LINUX_INSTALL