Add ARM builds

[NicoHood]

On ARM I cannot compile the library:

$ ./compile_linux.sh 
./compile_linux.sh: line 1: ./configure: No such file or directory
gcc: error: jnilib.c: No such file or directory
gcc: error: libserialport/linux_termios.c: No such file or directory
gcc: error: libserialport/linux.c: No such file or directory
gcc: error: libserialport/serialport.c: No such file or directory
gcc: fatal error: no input files
compilation terminated.
./compile_linux.sh: line 4: cd: libserialport: No such file or directory
gcc: error: jnilib.c: No such file or directory
gcc: error: libserialport/linux_termios.c: No such file or directory
gcc: error: libserialport/linux.c: No such file or directory
gcc: error: libserialport/serialport.c: No such file or directory
gcc: error: unrecognized command line option ‘-m32’
gcc: fatal error: no input files
compilation terminated.

This is expected, however you could fix it the way you prefere. All we need is an arm build hosted by arduino. I do not care if its cross compiled or not, but please add it if possible, as you did with arduino-builder.

Also please check the arduino-builder issue:
arduino/arduino-builder#79