PR server/18081: gdbserver crashes when providing an unexisting binary

$ ./gdbserver :1234 blah
 Process blah created; pid = 16471
 Cannot exec blah: No such file or directory.

 Child exited with status 127
 Killing process(es): 16471
 ../../../../src/binutils-gdb/gdb/gdbserver/linux-low.c:920: A problem internal to GDBserver has been detected.
 kill_wait_lwp: Assertion `res > 0' failed.

GDBserver shouldn't even be trying to kill that process.  GDBserver
kills or detaches from all processes on exit, and due to a missing
mourn_inferior call, GDBserver tries to kill the process that it had
already seen exit.

Tested on x86_64 Fedora 20.  New test included.  I emulated what
Windows outputs by hacking an error call in linux_create_inferior.

gdb/gdbserver/ChangeLog:
2015-05-06  Pedro Alves  <palves@redhat.com>

	PR server/18081
	* server.c (start_inferior): If the process exits, mourn it.

gdb/testsuite/ChangeLog:
2015-05-06  Pedro Alves  <palves@redhat.com>

	PR server/18081
	* gdb.server/non-existing-program.exp: New file.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,8 @@
+2015-05-06  Pedro Alves  <palves@redhat.com>
+
+	PR server/18081
+	* server.c (start_inferior): If the process exits, mourn it.
+
 2015-04-21  Gary Benson <gbenson@redhat.com>
 
 	* hostio.c (fileio_open_flags_to_host): Factored out to

gdb/gdbserver/server.c

@@ -284,6 +284,8 @@ start_inferior (char **argv)
       current_thread->last_resume_kind = resume_stop;
       current_thread->last_status = last_status;
     }
+  else
+    mourn_inferior (find_process_pid (ptid_get_pid (last_ptid)));
 
   return signal_pid;
 }

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2015-05-06  Pedro Alves  <palves@redhat.com>
+
+	PR server/18081
+	* gdb.server/non-existing-program.exp: New file.
+
 2015-05-05  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.ada/out_of_line_in_inlined.exp: Add run and "bt" tests.

gdb/testsuite/gdb.server/non-existing-program.exp

@@ -0,0 +1,63 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test starting gdbserver passing it the name of a non-existing
+# program.
+
+load_lib gdbserver-support.exp
+
+standard_testfile
+
+if { [skip_gdbserver_tests] } {
+    return 0
+}
+
+set gdbserver [find_gdbserver]
+if { $gdbserver == "" } {
+    fail "could not find gdbserver"
+    return
+}
+
+# Fire off gdbserver.  The port doesn't really matter, gdbserver tries
+# to spawn the program before opening the connection.
+set spawn_id [remote_spawn target "$gdbserver stdio non-existing-program"]
+
+set msg "gdbserver exits cleanly"
+set saw_exiting 0
+expect {
+    # This is what we get on ptrace-based targets.
+    -re "stdin/stdout redirected.*No program to debug\r\nExiting\r\n$" {
+	set saw_exiting 1
+	exp_continue
+    }
+    # This is what we get on Windows.
+    -re "Error creating process\r\n\r\nExiting\r\n$" {
+	set saw_exiting 1
+	exp_continue
+    }
+    -re "A problem internal to GDBserver has been detected" {
+	fail "$msg (GDBserver internal error)"
+	wait
+    }
+    eof {
+	gdb_assert $saw_exiting $msg
+	wait
+    }
+    timeout {
+	fail "$msg (timeout)"
+    }
+}