fwrite performance improved significantly.
Stewart Brodie authored
  Another getenv() bug fixed.
Detail:
  stdio.c contains a vastly improved implementation of fwrite.
  hostsys.h declares _terminate_getenv to remove build warnings.
  armsys.c contains fix to getenv() to stop Omni dying.
Admin:
  Tested on desktop machine for over a week without incident, including
    several heavy fwrite users (WebServe, C compiler)
  fwrite change is documented in Doc/fwrite
  getenv() bug is Bugzilla bug #28

Version 5.27. Tagged as 'RISC_OSLib-5_27'
0bb3e26a