gdb/testsuite: support passing inferior arguments with native-gdbserver board

gdb/testsuite: support passing inferior arguments with native-gdbserver board

This patch makes it possible to run tests requiring passing arguments to
the inferior with the native-gdbserver board.  The end goal is to write
a test that verifies passing arguments to the inferior works, and to
have that test exercise inferior arguments passed on the gdbserver
command line, when using the native-gdbserver target board (in addition
to the other boards).  This is done in the next patch.

With the native-gdbserver target board, gdbserver is started in
gdb_reload (implemented in config/gdbserver.exp), called in gdb_run_cmd.
gdb_run_cmd already supposedly accepts inferior arguments (although that
feature does not seem to be used anywhere), which it passes to the `run`
command, for non-stub target boards.  I've changed gdb_run_cmd so that
it forwards these arguments to gdb_reload as well.  gdb_reload passes
them to gdbserver_run, and they eventually make their way to the
gdbserver command line.

gdb_run_cmd currently accepts `args` (the varargs of tcl), which means
it receives inferior arguments as a list.  This won't work with
arguments with spaces, because they will end up being formatted with
curly braces like this:

    % set args [list hello "with spaces" world]
    hello {with spaces} world
    % puts "run $args"
    run hello {with spaces} world

I've changed it to accept a single string that is passed to `run` and
gdb_reload.  I've done the same change in gdb_start_cmd and
gdb_starti_cmd, although these two are not used with native-gdbserver.

I've changed all gdb_reload implementations in the tree to accept a new
inferior_args argument, although most of them don't do anything with it
(and don't need to).  People maintaining target boards out of tree will
need to do the same.

I found two tests to adjust to avoid adding new failures or errors.
These tests needed new [use_gdb_stub] checks, because they rely on
having GDB run new processes.  These are guarded by a [target_info
exists noargs], which made them get skipped on native-gdbserver.  But
now that the native-gdbserver board supports args, this is no longer
enough.

Note that with this change, noargs and use_gdb_stub are orthogonal.  It
took me a moment to grasp this, so I thought I would spell out the
different possible situations:

- !noargs and !use_gdb_stub: inferior process started by gdb, can pass
  args
- noargs and !use_gdb_stub: inferior process started by gdb (perhaps
  through extended-remote protocol, the simulator, some other target),
  but that target doesn't support inferior arguments
- noargs and use_gdb_stub: inferior process started by some other
  program to which GDB connects using the remote protocol, that program
  does not support passing args to the inferior process
- !noargs and use_gdb_stub: inferior process started by some other
  program to which GDB connects u sing the remote protocol, that program
  supports passing args to the inferior process

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (gdb_run_cmd): Change argument from args to
	inferior_args.  Pass it to gdb_reload.
	(gdb_start_cmd, gdb_starti_cmd): Change argument from args to
	inferior_args.
	(gdb_reload): Add inferior_args argument.
	* config/gdbserver.exp (gdb_reload): Add inferior_args argument,
	pass it to gdbserver_run.
	* boards/native-gdbserver.exp: Do not set noargs.
	* boards/native-extended-gdbserver.exp (gdb_reload): Add
	inferior_args argument.
	* boards/stdio-gdbserver-base.exp (gdb_reload): Likewise.
	* gdb.base/a2-run.exp: Check for use_gdb_stub.
	* gdb.base/args.exp: Likewise.

Change-Id: Ibda027c71867157852f34700342ab31edf39e4d8