gdb: fix display of thread condition for multi-location breakpoints

gdb: fix display of thread condition for multi-location breakpoints

This commit addresses the issue in PR gdb/30087.

If a breakpoint with multiple locations has a thread condition, then
the 'info breakpoints' output is a little messed up, here's an example
of the current output:

  (gdb) break foo thread 1
  Breakpoint 2 at 0x401114: foo. (3 locations)
  (gdb) break bar thread 1
  Breakpoint 3 at 0x40110a: file /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c, line 32.
  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  2       breakpoint     keep y   <MULTIPLE>          thread 1
          stop only in thread 1
  2.1                         y   0x0000000000401114 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  2.2                         y   0x0000000000401146 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  2.3                         y   0x0000000000401168 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  3       breakpoint     keep y   0x000000000040110a in bar at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:32 thread 1
          stop only in thread 1

Notice that, at the end of the location for breakpoint 3, the 'thread
1' condition is printed, but this is then repeated on the next line
with 'stop only in thread 1'.

In contrast, for breakpoint 2, the 'thread 1' appears randomly, in the
"What" column, though slightly offset, non of the separate locations
have the 'thread 1' information.  Additionally for breakpoint 2 we
also get a 'stop only in thread 1' line.

There's two things going on here.  First the randomly placed 'thread
1' for breakpoint 2 is due to a bug in print_one_breakpoint_location,
where we check the variable part_of_multiple instead of
header_of_multiple.

If I fix this oversight, then the output is now:

  (gdb) break foo thread 1
  Breakpoint 2 at 0x401114: foo. (3 locations)
  (gdb) break bar thread 1
  Breakpoint 3 at 0x40110a: file /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c, line 32.
  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  2       breakpoint     keep y   <MULTIPLE>
          stop only in thread 1
  2.1                         y   0x0000000000401114 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25 thread 1
  2.2                         y   0x0000000000401146 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25 thread 1
  2.3                         y   0x0000000000401168 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25 thread 1
  3       breakpoint     keep y   0x000000000040110a in bar at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:32 thread 1
          stop only in thread 1

The 'thread 1' condition is now displayed at the end of each location,
which makes the output the same for single location breakpoints and
multi-location breakpoints.

However, there's still some duplication here.  Both breakpoints 2 and
3 include a 'stop only in thread 1' line, and it feels like the
additional 'thread 1' is redundant.  In fact, there's a comment to
this very effect in the code:

  /* FIXME: This seems to be redundant and lost here; see the
     "stop only in" line a little further down.  */

So, lets fix this FIXME.  The new plan is to remove all the trailing
'thread 1' markers from the CLI output, we now get this:

  (gdb) break foo thread 1
  Breakpoint 2 at 0x401114: foo. (3 locations)
  (gdb) break bar thread 1
  Breakpoint 3 at 0x40110a: file /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c, line 32.
  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  2       breakpoint     keep y   <MULTIPLE>
          stop only in thread 1
  2.1                         y   0x0000000000401114 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  2.2                         y   0x0000000000401146 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  2.3                         y   0x0000000000401168 in foo at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:25
  3       breakpoint     keep y   0x000000000040110a in bar at /tmp/src/gdb/testsuite/gdb.base/thread-bp-multi-loc.c:32
          stop only in thread 1

All of the above points are also true for the Ada 'task' breakpoint
condition, and the changes I've made also update how the task
information is printed, though in the case of the Ada task there was
no 'stop only in task XXX' line printed, so I've added one of those.

Obviously it can't be quite that easy.  For MI backwards compatibility
I've retained the existing code (but now only for MI like outputs),
which ensures we should generate backwards compatible output.

I've extended an Ada test to cover the new task related output, and
updated all the tests I could find that checked for the old output.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30087

Approved-By: Pedro Alves <pedro@palves.net>