[RFC] gdb.cp/static-print-quit.exp: fix racy tests (PR testsuite/12649)

[Marek Polacek <mpolacek at redhat dot com>]

This test fails with Jan's read1() with:

ERROR: Window too small.
UNRESOLVED: gdb.cp/static-print-quit.exp: print c

This is because we expect to read:
"...Type <return> to continue, or q <return> to quit---$"

However, when using read1(), the "<return>" part matches with
this snippet from lib/gdb.exp:

         "<return>" {
            send_gdb "\n"
            perror "Window too small."
            fail "$message"
            ...

We can prevent this if we, in our gdb_test_multiple, create a "<return>"
case with `exp_continue'.  Nonetheless, except this, we must also in this
case:

    -re " to quit---$" {
        fail $test
        return -1
    }

differentiate between success and failure, since after processing the "<return>"
part we now have in the buffer " to quit---".  Thus, it is possible to do
something like this, using a new variable `seen_return', although I must say, I don't
like it at all.  But I don't see any other way how to cure this (at least yet) without
modifying the lib/gdb.exp.  Ran the test with both read{,1}.  Comments or complaints, please?

set test "print c"
set seen_return 0
gdb_test_multiple $test $test {
    "<return>" {
	incr seen_return
	exp_continue
    }
    -re "\\$\[0-9\]+ = \{loooooooooooooooooooooooooooooooooooooooooooooong = 0, static field = \{\r\n---Type " {
	incr seen_return
	exp_continue
    }
    -re " to continue, or q " {
	incr seen_return
	exp_continue
    }
    -re " to quit---$" {
        if { $seen_return >= 2 } {
	    pass $test
	} else { 
            fail $test
            return -1
	}
    }
}

Thanks,

	Marek