reverted forcing travis to install `gcc-arm-none-eabi=4-*`
Merge pull request #1742 from BytesGalore/revert_workaround_for_gcc_arm_none

Travis: reverted forcing travis to install `gcc-arm-none-eabi=4-*`
travis: remove comment obsoleted by #1742
Merge pull request #1743 from N8Fear/travis

travis: remove comment obsoleted by #1742
added empty _kill() stub
removed _kill_r() function already implemented in newlib
un-blacklisted msba2 from `riot_and_cpp`
added missing CXX exports