- Add libstdcpp feature to indicate a platform is providing a libstdc++
implementation ready for use
- The existing cpp feature now only indicates a working C++ toolchain without
libstdc++. (E.g. still useful for the Arduino compatibility layer.)
- Added libstdcpp as required feature were needed
- Added some documentation on C++ on RIOT
puf_sram only relies on an uninitialized chunk of memory.
This means to enable it we just have to hook up puf_sram_init().
All memory after __bss_end should be uninitialized at startup, so
just use that.
