testsuite: refactor spawn and wait for attach

Several places in the testsuite have a copy of a snippet of code that
spawns a test program, waits a bit, and then does some PID munging for
Cygwin.  This is in order to have GDB attach to the spawned program.

This refactors all that to a common procedure.

(multi-attach.exp wants to spawn multiple processes, so this makes the
new procedure's interface work with lists.)

Tested on x86_64 Fedora 20.

gdb/testsuite/ChangeLog:
2014-09-11  Pedro Alves  <palves@redhat.com>

	* lib/gdb.exp (spawn_wait_for_attach): New procedure.
	* gdb.base/attach.exp (do_attach_tests, do_call_attach_tests)
	(do_command_attach_tests): Use spawn_wait_for_attach.
	* gdb.base/solib-overlap.exp: Likewise.
	* gdb.multi/multi-attach.exp: Likewise.
	* gdb.python/py-prompt.exp: Likewise.
	* gdb.python/py-sync-interp.exp: Likewise.
	* gdb.server/ext-attach.exp: Likewise.
gdb/17347 - Regression: GDB stopped on run with attached process

Doing:

  gdb --pid=PID -ex run

Results in GDB getting a SIGTTIN, and thus ending stopped.  That's
usually indicative of a missing target_terminal_ours call.

E.g., from the PR:

 $ sleep 1h & p=$!; sleep 0.1; gdb -batch sleep $p -ex run
 [1] 28263
 [1]   Killed                  sleep 1h

 [2]+  Stopped                 gdb -batch sleep $p -ex run

The workaround is doing:

 gdb -ex "attach $PID" -ex "run"

instead of

 gdb [-p] $PID -ex "run"

With the former, gdb waits for the attach command to complete before
moving on to the "run" command, because the interpreter is in sync
mode at this point, within execute_command.  But for the latter,
attach_command is called directly from captured_main, and thus misses
that waiting.  IOW, "run" is running before the attach continuation
has run, before the program stops and attach completes.  The broken
terminal settings are just one symptom of that.  Any command that
queries or requires input results in the same.

The fix is to wait in catch_command_errors (which is specific to
main.c nowadays), just like we wait in execute_command.

gdb/ChangeLog:
2014-09-11  Pedro Alves  <palves@redhat.com>

	PR gdb/17347
	* main.c: Include "infrun.h".
	(catch_command_errors, catch_command_errors_const): Wait for the
	foreground command to complete.
	* top.c (maybe_wait_sync_command_done): New function, factored out
	from ...
	(maybe_wait_sync_command_done): ... here.
	* top.h (maybe_wait_sync_command_done): New declaration.

gdb/testsuite/ChangeLog:
2014-09-11  Pedro Alves  <palves@redhat.com>

	PR gdb/17347
	* lib/gdb.exp (gdb_spawn_with_cmdline_opts): New procedure.
	* gdb.base/attach.exp (test_command_line_attach_run): New
	procedure.
	(top level): Call it.
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