Tweak gdb.base/async.exp

Tweak gdb.base/async.exp

I see two fails in async.exp on arm-none-eabi target:

nexti&^M
(gdb) 0x000001ba        14       x = 5; x = 5;^M
completed.^M
FAIL: gdb.base/async.exp: nexti&
finish&^M
Run till exit from #0  0x000001ba in foo () at /scratch/yqi/arm-none-eabi-lite/src/gdb-trunk/gdb/testsuite/gdb.base/async.c:14^M
(gdb) 0x000001e6 in main () at /scratch/yqi/arm-none-eabi-lite/src/gdb-trunk/gdb/testsuite/gdb.base/async.c:32^M
32       y = foo ();^M
Value returned is $1 = 8^M
completed.^M
FAIL: gdb.base/async.exp: finish&

The corresponding test is "test_background "nexti&" "" ".*y = 3.*"",
and it assumes that GDB "nexti" into the next source line.  It is wrong
on arm.  After "nexti", it still stops at the same source line, and it
fails.

When gdb does "finish", if the PC is in the middle of a source line,
the PC address is printed too.  See stack.c:print_frame,

  if (opts.addressprint)
    if (!sal.symtab
	|| frame_show_address (frame, sal)
	|| print_what == LOC_AND_ADDRESS)
      {
	annotate_frame_address ();
	if (pc_p)
	  ui_out_field_core_addr (uiout, "addr", gdbarch, pc);
	else
	  ui_out_field_string (uiout, "addr", "<unavailable>");
	annotate_frame_address_end ();
	ui_out_text (uiout, " in ");
      }

frame_show_address checks whether PC is the middle of a source line.
Since after "nexti", the inferior stops at the middle of a source line,
when we do "finish" the PC address is displayed.

In sum, GDB works well, but test case needs update.  This patch is to
add a statement at the same line to make sure "nexti" doesn't go to
the new line, match the next instruction address in the output and
match the hex address the output of "finish".

gdb/testsuite:

2014-06-06  Yao Qi  <yao@codesourcery.com>

	* gdb.base/async.c (foo): Add one statement.
	* gdb.base/async.exp: Get the next instruction address and
	match the output of "nexti" by instruction address.  Match
	the hex address in the output of "finish".