cpu/stm32f0: c++: initial support for c++, added _kill (weak) and weak attribute for _kill_r
boards/stm32f0discovery: provided c++ feature (cpp)
Merge pull request #1987 from BytesGalore/EasyCPPMixing_stm32f0discovery_support_fix

cpu/stm32f0 C++ stmf0discovery support fix