include "cpu.h" for MSP430 platforms in fd.h
changed condition in fd.c to check for MCU instead of checking for the board
removed own implementation of errno headers
making socket.h MSP430 ready
osx fixes
Merge pull request #533 from LudwigOrtmann/osx_fixes

osx fixes
Merge pull request #521 from OlegHahm/fix_includes_for_msp430

Fix includes for msp430