[HEADS-UP] gdb segfault

[Michael Snyder <msnyder@redhat.com>]

Hey yo --

gdb is seg-faulting immediately whenever its run with --noasync.
I have an old build from the beginning of March that doesn't
do it (nor do even older ones), so it's probably a change
from between then and now.

It crashes in display_gdb_prompt, as called from
tui_command_loop.  Here's a backtrace.


#0  0x40106d33 in strlen () from /lib/tls/libc.so.6
#1  0x08114c6a in display_gdb_prompt (new_prompt=0x0)
     at /home/msnyder/src/gdb/event-top.c:280
#2  0x080bf1f5 in tui_command_loop (data=0x0)
     at /home/msnyder/src/gdb/tui/tui-interp.c:140
#3  0x0811168a in current_interp_command_loop ()
     at /home/msnyder/src/gdb/interps.c:277
#4  0x0807aafb in captured_command_loop (data=0x0)
     at /home/msnyder/src/gdb/main.c:97
#5  0x080801d9 in do_catch_errors (uiout=0x830b0c0, data=0xbfffbe18)
     at /home/msnyder/src/gdb/top.c:524
#6  0x0807ffdc in catcher (func=0x80801bd <do_catch_errors>,
     func_uiout=0x830b0c0, func_args=0xbfffbe18, func_val=0xbfffbe24,
     func_caught=0xbfffbe20, errstring=0x822cc48 "", gdberrmsg=0x0, mask=6)
     at /home/msnyder/src/gdb/top.c:431
#7  0x08080214 in catch_errors (func=0x807aaf0 <captured_command_loop>,
     func_args=0x0, errstring=0x822cc48 "", mask=6)
     at /home/msnyder/src/gdb/top.c:536
#8  0x0807b918 in captured_main (data=0xbfffc140)
     at /home/msnyder/src/gdb/main.c:805
#9  0x080801d9 in do_catch_errors (uiout=0x82b8220, data=0xbfffc0f8)
     at /home/msnyder/src/gdb/top.c:524
#10 0x0807ffdc in catcher (func=0x80801bd <do_catch_errors>,
     func_uiout=0x82b8220, func_args=0xbfffc0f8, func_val=0xbfffc104,
     func_caught=0xbfffc100, errstring=0x822cc48 "", gdberrmsg=0x0, mask=6)
     at /home/msnyder/src/gdb/top.c:431
#11 0x08080214 in catch_errors (func=0x807ab2e <captured_main>,
     func_args=0xbfffc140, errstring=0x822cc48 "", mask=6)
     at /home/msnyder/src/gdb/top.c:536
#12 0x0807b942 in gdb_main (args=0xbfffc140)
     at /home/msnyder/src/gdb/main.c:814
#13 0x0807aae9 in main (argc=2, argv=0xbfffc1e4)
     at /home/msnyder/src/gdb/gdb.c:35