[ping] fix VXWORKS_LIBGCC_SPEC not to include -lc_internal for shared rtps

[Olivier Hainque]

Hello,

Ping for https://gcc.gnu.org/ml/gcc-patches/2015-12/msg02028.html

>       * config/vxworks.h (VXWORKS_LIBGCC_SPEC): Don't link shared RTPs with
>       libc_internal.

Thanks in advance,

With Kind Regards,

Olivier