Jit, testsuite: Amend expect processing to tolerate more platforms.

The current 'fixed_host_execute' implementation fails on Darwin
platforms for a number of reasons:

1/ If the sub-process spawn fails (e.g. because of missing or mal-
   formed params); rather than reporting the fail output into the
   match stream, as indicated by the expect manual, it terminates
   the script.

 - We fix this by (a) checking that the executable is valid as well
   as existing (b) we put the spawn into a catch block and report
   a failure.

2/ There is no recovery path at all for a buffer-full case (and we
   do see buffer-full events with the default sizes).

 - Added by the patch here, however it is not as sophisticated as
   the methods used by dejagnu internally.  Here we set the process
   to be "nowait" and then close the connection - with the intent
   that this will terminate the spawned process.

3/  The expect logic assumes that 'Totals:' is a valid indicator
    for the end of the spawned process output.  This is not true
    even for the default dejagnu header (there are a number of
    additional reporting lines after).  In addition to this, there
    are some tests that intentionally produce more output after
    the totals report (and there are tests that do not use that
    mechanism at all).

    The effect is the we might arrive at the "wait" for the spawned
    process to finish - but that process might not have completed
    all its output.  For Darwin, at least that causes a deadlock
    between expect and the spawnee - the latter is doing a non-
    cancellable write and the former is waiting for the latter to
    terminate.  For some reason this does not seem to affect Linux
    perhaps the pty implementation allows the write(s) are able to
    proceed even though there is no reader.

 -  This is fixed by modifying the loop termination condition to be
    either EOF (which will be the 'correct' condition) or a timeout
    which would represent an error either in the runtime or in the
    parsing of the output.  As added precautions, we only try to
    wait if there is a correcly-spawned process, and we are also
    specific about which process we are waiting for.

4/  Darwin appears to have a bug in either the tcl or termios
    'cooking' code that ocassionally inserts an additional CR char
    into the stream - thus '\n' => '\r\r\n' instead of '\r\n'. The
    original program output is correct (it only contains a single
    \n) - the additional character is being inserted somewhere in
    the translations applied before the output reaches expect.

    The logic of this expect implementation does not tolerate single
    \r or \n characters (it will fail with a timeout or buffer-full
    if that occurs).

 -  This is fixed by having a line-end match that is adjusted for
    Darwin.

5/  The default buffer size does seem to be too small in some cases
    noting that GCC uses 10000 as the match buffer size and the
    default is 2000.

 -  Fixed by increasing the size to 8192.

6/  There is a somewhat arbitrary dumping of output where we match
    ^$prefix\tSOMETHING... and then process the something.  This
    essentially allows the match to start at any place in the buffer
    following any collection of non-line-end chars.

 -  Fixed by amending the match for 'general' lines to accommodate
    these cases, and reporting such lines to the log.  At least this
    should allow debugging of any cases where output that should be
    recognized is being dropped.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/testsuite/ChangeLog:

	* jit.dg/jit.exp (fixed_local_execute): Amend the match and
	exit conditions to cater for more platforms.

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