🚀 go-pugleaf

I tried to compile GDB 4.6 on Interactive Unix 2.2.1, a system
V-based-but-supposedly-POSIX system, and had a few troubles, which I
will detail in separate messages following.

I did `configure i386-sysv'.

With the subsequent changes, the resulting gdb executable apparently
works.  ld gives one warning:
ld warning: Multiply defined symbol PC, in /usr/lib/libtermcap.a, has more than one size
but this doesn't make any difference.

More compiler flags need to be used on this system (at least when
compiling with gcc).

Specifically:

* -posix (to get POSIX support)  [-Xp for cc, although I didn't try to
  compile with cc]

* -DHAVE_UNISTD_H

* -DUSG [for the libraries -- gdb/xm-i386v.h unconditionally defines
         USG, thus yielding annoying warnings when I define it on the
         command line.  I think this will go away if USG was defined by
         configure, though.]

* -DTIOCGETC_BROKEN -DTIOCGLTC_BROKEN (actually, I think it's not so
  much that TIOCG* is broken, but that the right header files aren't
  being included in the right order -- ISC has both termio and termios
  and sgtty and everything else under the sun -- but defining these at
  least lets things compile).

I would have liked to modify the configure scripts so that these things
would happen automatically with `configure i386-isc2.2*', but I couldn't
sufficiently comprehend how they worked.

Although the -posix perhaps cannot be determined automatically, it seems
to me that it would be better configure simplyed look to see if there is
a <unistd.h>, instead of having to do the define or not for every
possible system.  I think the libg++ configure does this (or at least it
does similar things), so maybe that will happen automatically in 4.7.

Likewise for TIO stuff ... it seems to me it would be straightforward to
check that automatically.  (Just try to compile whatever construct is
now #ifdef'd, and if it doesn't work, define the *_BROKEN switch.)

By the way, in gdb/main.c I saw the following:

#ifdef USG
#include <sys/types.h>
#include <unistd.h>
#endif

I think this is intended to be conditionalized on HAVE_UNISTD_H, not USG.