make dprintf.exp pass in target async mode

When target-async is enabled, dprintf.exp fails:

 Running ../../../src/gdb/testsuite/gdb.base/dprintf.exp ...
 FAIL: gdb.base/dprintf.exp: 1st dprintf, call
 FAIL: gdb.base/dprintf.exp: 2nd dprintf, call
 FAIL: gdb.base/dprintf.exp: Set dprintf function
 FAIL: gdb.base/dprintf.exp: 1st dprintf, fprintf
 FAIL: gdb.base/dprintf.exp: 2nd dprintf, fprintf

 Breakpoint 2, main (argc=1, argv=0x7fffffffd3f8) at ../../../src/gdb/testsuite/gdb.base/dprintf.c:33
 33        int loc = 1234;
 (gdb) continue
 Continuing.
 kickoff 1234
 also to stderr 1234
 At foo entry
 (gdb) FAIL: gdb.base/dprintf.exp: 1st dprintf, call

The problem is that GDB gave the prompt back to the user too early.

This happens when calling functions while handling an event that
doesn't cause a user visible stop.  dprintf with "set dprintf-style
gdb" is one such case.  This patch adds a test case that has a
breakpoint with a condition that calls a function that returns false,
so that regression testing isn't dependent on the implementation of
dprintf.

The problem happens because run_inferior_call causes GDB to forget
that it is running in sync_execution mode, so any event that runs an
inferior call causes fetch_inferior_event to display the prompt, even
if the event should not result in a user visible stop (that is, gdb
resumes the inferior and waits for the next event).

This patch fixes the issue by noticing when GDB was in sync_execution
mode in run_inferior_call, and taking care to restore this state
afterward.

gdb/
2014-03-20  Tom Tromey  <tromey@redhat.com>

	PR cli/15718
	* infcall.c: Include event-top.h.
	(run_inferior_call): Call async_disable_stdin if needed.

gdb/testsuite/
2014-03-20  Tom Tromey  <tromey@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	PR cli/15718
	* gdb.base/condbreak-call-false.c: New file.
	* gdb.base/condbreak-call-false.exp: New file.
Fix py-finish-breakpoint.exp with target async.

With target async enabled, py-finish-breakpoint.exp triggers an
assertion failure.

The failure occurs because execute_command re-enters the event loop in
some circumstances, and in this case resets the sync_execution flag.
Then later GDB reaches this assertion in normal_stop:

      gdb_assert (sync_execution || !target_can_async_p ());

In detail:

#1 - A synchronous execution command is run.  sync_execution is set.

#2 - A python breakpoint is hit (TARGET_WAITKIND_STOPPED), and the
     corresponding Python breakpoint's stop method is executed.  When
     and while python commands are executed, interpreter_async is
     forced to 0.

#3 - The Python stop method happens to execute a not-execution-related
     gdb command.  In this case, "where 1".

#4 - Seeing that sync_execution is set, execute_command nests a new
     event loop (although that wasn't necessary; this is the problem).

#5 - The linux-nat target's pipe in the event loop happens to be
     marked.  That's normal, due to this in linux_nat_wait:

     /* If we requested any event, and something came out, assume there
        may be more.  If we requested a specific lwp or process, also
        assume there may be more.  */

     The nested event loop thus immediately wakes up and calls
     target_wait.  No thread is actually executing in the inferior, so
     the target returns TARGET_WAITKIND_NO_RESUMED.

#6 - normal_stop is reached.  GDB prints "No unwaited-for children
     left.", and resets the sync_execution flag (IOW, there are no
     resumed threads left, so the synchronous command is considered
     completed.)  This is already bogus.  We were handling a
     breakpoint!

#7 - the nested event loop unwinds/ends.  GDB is now back to handling
     the python stop method (TARGET_WAITKIND_STOPPED), which decides
     the breakpoint should stop.  normal_stop is called for this
     event.  However, normal_stop actually works with the _last_
     reported target status:

   void
   normal_stop (void)
   {
    struct target_waitstatus last;
    ptid_t last_ptid;
    struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);

    ...
    get_last_target_status (&last_ptid, &last);

    ...
    if (last.kind == TARGET_WAITKIND_NO_RESUMED)
      {
        gdb_assert (sync_execution || !target_can_async_p ());

        target_terminal_ours_for_output ();
        printf_filtered (_("No unwaited-for children left.\n"));
      }

   And due to the nesting in execute command, the last event is now
   TARGET_WAITKIND_NO_RESUMED, not the actual breakpoint event being
   handled.  This could be seen to be broken in itself, but we can
   leave fixing that for another pass.  The assertion is reached, and
   fails.

execute_command has a comment explaining when it should synchronously
wait for events:

      /* If the interpreter is in sync mode (we're running a user
	 command's list, running command hooks or similars), and we
	 just ran a synchronous command that started the target, wait
	 for that command to end.  */

However, the code did not follow this comment -- it didn't check to
see if the command actually started the target, just whether the
target was executing a sync command at this point.

This patch fixes the problem by noting whether the target was
executing in sync_execution mode before running the command, and then
augmenting the condition to test this as well.

2014-03-20  Tom Tromey  <tromey@redhat.com>

	PR gdb/14135
	* top.c (execute_command): Only dispatch events if the command
	started the target.