Fix "layout reg" crash

Fix "layout reg" crash

Commit d7e747318f4d04 ("Eliminate make_cleanup_ui_file_delete / make
ui_file a class hierarchy") introduced a problem when using "layout
regs", that leads gdb to crash when issuing:

./gdb ./a.out -ex 'layout regs' -ex start

From the backtrace, it's caused by this 'delete' on tui_restore_gdbout():

 (gdb) bt
 #0  0x00007ffff6b962b2 in free () from /lib64/libc.so.6
 #1  0x000000000059fa47 in tui_restore_gdbout (ui=0x22997b0) at ../../gdb/tui/tui-regs.c:714
 #2  0x0000000000619996 in do_my_cleanups (pmy_chain=pmy_chain@entry=0x1e08320 <cleanup_chain>, old_chain=old_chain@entry=0x235b4b0) at ../../gdb/common/cleanups.c:154
 #3  0x0000000000619b1d in do_cleanups (old_chain=old_chain@entry=0x235b4b0) at ../../gdb/common/cleanups.c:176
 #4  0x000000000059fb0d in tui_register_format (frame=frame@entry=0x22564e0, regnum=regnum@entry=0) at ../../gdb/tui/tui-regs.c:747
 #5  0x000000000059ffeb in tui_get_register (data=0x2434d18, changedp=0x0, regnum=0, frame=0x22564e0) at ../../gdb/tui/tui-regs.c:768
 #6  tui_show_register_group (refresh_values_only=<optimized out>, frame=0x22564e0, group=0x1e09250 <general_group>) at ../../gdb/tui/tui-regs.c:287
 #7  tui_show_registers (group=0x1e09250 <general_group>) at ../../gdb/tui/tui-regs.c:156
 #8  0x00000000005a07cf in tui_check_register_values (frame=frame@entry=0x22564e0) at ../../gdb/tui/tui-regs.c:496
 #9  0x00000000005a3e65 in tui_check_data_values (frame=frame@entry=0x22564e0) at ../../gdb/tui/tui-windata.c:232
 #10 0x000000000059cf65 in tui_refresh_frame_and_register_information (registers_too_p=1) at ../../gdb/tui/tui-hooks.c:156
 #11 0x00000000006d5c05 in generic_observer_notify (args=0x7fffffffdbe0, subject=<optimized out>) at ../../gdb/observer.c:167
 #12 observer_notify_normal_stop (bs=<optimized out>, print_frame=print_frame@entry=1) at ./observer.inc:61
 #13 0x00000000006a6409 in normal_stop () at ../../gdb/infrun.c:8364
 #14 0x00000000006af8f5 in fetch_inferior_event (client_data=<optimized out>) at ../../gdb/infrun.c:3990
 #15 0x000000000066f0fd in gdb_wait_for_event (block=block@entry=0) at ../../gdb/event-loop.c:859
 #16 0x000000000066f237 in gdb_do_one_event () at ../../gdb/event-loop.c:322
 #17 0x000000000066f386 in gdb_do_one_event () at ../../gdb/event-loop.c:353
 #18 0x00000000007411bc in wait_sync_command_done () at ../../gdb/top.c:570
 #19 0x0000000000741426 in maybe_wait_sync_command_done (was_sync=0) at ../../gdb/top.c:587
 #20 execute_command (p=<optimized out>, p@entry=0x7fffffffe43a "start", from_tty=from_tty@entry=1) at ../../gdb/top.c:676
 #21 0x00000000006c2048 in catch_command_errors (command=0x741200 <execute_command(char*, int)>, arg=0x7fffffffe43a "start", from_tty=1) at ../../gdb/main.c:376
 #22 0x00000000006c2b60 in captured_main_1 (context=0x7fffffffde70) at ../../gdb/main.c:1119
 #23 captured_main (data=0x7fffffffde70) at ../../gdb/main.c:1140
 #24 gdb_main (args=args@entry=0x7fffffffdf90) at ../../gdb/main.c:1158
 #25 0x0000000000408cf5 in main (argc=<optimized out>, argv=<optimized out>) at ../../gdb/gdb.c:32
 (gdb) f 1
 #1  0x000000000059fa47 in tui_restore_gdbout (ui=0x22997b0) at ../../gdb/tui/tui-regs.c:714
 714	  delete gdb_stdout;

The problem is simply that the commit mentioned above made the ui_file
that gdb_stdout is temporarily set to be a stack-allocated
string_file, while before it used to be a heap-allocated ui_file.  The
fix is simply to remove the now-incorrect delete.

New test included, which exercises enabling all TUI layouts, with and
without execution.  (This particular crash only triggers with
execution.)

gdb/ChangeLog:
2017-03-07  Pedro Alves  <palves@redhat.com>

	* tui/tui-regs.c (tui_restore_gdbout): Don't delete gdb_stdout.

gdb/testsuite/ChangeLog:
2017-03-07  Pedro Alves  <palves@redhat.com>

	* gdb.base/tui-layout.c: New file.
	* gdb.base/tui-layout.exp: New file.