community/gcc-cross-embedded: Split out C++ support to community/g++-cross-embedded

This allows building without a preliminary newlib installed, allowing to drop the newlib-stage1 and, therefore, the gcc-cross-embedded-stage1 package. The goal is to provide C++ support as separate g++-cross-embedded package.

In addition to get rid of the uglyness of those stage1 pkgs only needed as build dependencies and useless for users, this safes a bit of build time and a bit of disk space for users not interested in embedded C++ development.