log_writer_file: add include px4_posix.h (needed for stack size macro)
log_writer_file: add include px4_posix.h (needed for stack size macro)

Failed with GCC 6.0.1, don't know why it worked before...

krbeverx/Firmware,PX4/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,Aerotenna/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,Aerotenna/Firmware,PX4/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,jlecoeur/Firmware,dagar/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,PX4/Firmware,Aerotenna/Firmware,PX4/Firmware,jlecoeur/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,acfloria/Firmware,acfloria/Firmware,dagar/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,acfloria/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,jlecoeur/Firmware