exchanged BOARD_BLACKLIST with FEATURES_REQUIRED in the example Makefile
added cpp as feature for board native
Merge pull request #1988 from BytesGalore/riot_and_cpp_blacklist_to_required_feature

examples/riot_and_cpp: exchanged BOARD_BLACKLIST with FEATURES_REQUIRED
removed _kill_r() from syscalls (due to provided by precompiled gnu toolchain)
added kill_r() to syscalls (due to required by newlib)
unblacklisted board from example Makefile
added CXX flags to board Makefile
[SQUASH ME] added cpp feature to stm32f4discovery board