This fixes building tests/pkg_arduino_sdi_12 for the hifive1b board.
The problem is, in build/pkg/arduino_api/api/Common.h millis is defined
within an extern "C" block. While in sys/arduino/include/arduino.hpp it
was not.
This fixes the error:
$ BOARD=arduino-mega2560 make -C tests/pkg_arduino_sdi_12/
[...]
[...]/RIOT/build/pkg/arduino_sdi_12/src/SDI12.cpp:379:7: error: ‘interrupts’ was not declared in this scope
To make it possible to use an Arduino library, a new pseudomodule arduino_lib is introduced. This pseudomodule enables implicitly module arduino but avoids that a sketch is required or generated and compiled. Thus, it is possible to compile and use a package or directory with some source files from an Arduino library in RIOT applications.
Arduino libraries often include Arduino.h. For source code compatibility this header file is required. Header guards in file arduino.hpp had to be renamed.
