small libf2c cleanups

[Jeffrey A Law]

  In message < 19971014194418.35064@dot.cygnus.com >you write:
  > Two of the changes are basicly covered by autoconf.  The signal_.c
  > change avoids casting a DImode pointer to SImode int on Alpha.  I
  > have no idea what the function is supposed to return, but what it
  > had been doing made no sense to me.
  > 
  > 
  > r~
  > 
  > 
  > 
  > Tue Oct 14 19:40:34 1997  Richard Henderson  <rth@cygnus.com>
  > 
  > 	* libF77/signal_.c (G77_signal_0): Make return type sig_pf as well.
  > 	* libI77/fio.h: Include <string.h> if STDC_HEADERS.
  > 	* libU77/chmod_.c: Likewise.
Installed.  We'll have to keep an eye on the signal stuff -- I'm not
100% sure of what we want to do with it either.

jeff