* top.c (gdb_readline): Allow CRLF line termination on systems

* top.c (gdb_readline): Allow CRLF line termination on systems
which define CRLF_SOURCE_FILES.
* win32-nat.c: 1) Add thread support, 2) fix ability to attach to
a running process, and 3) implement limited support for cygwin
signals.
(thread_rec): New function.
(child_add_thread): Ditto.
(child_init_thread_list): Ditto.
(child_delete_thread): Ditto.
(do_child_fetch_inferior_registers): Ditto.
(do_child_store_inferior_registers): Ditto.
(handle_output_debug_string): Ditto.
(child_fetch_inferior_registers): Use do_* function to perform
operation.
(child_store_inferior_registers): Ditto.
(child_continue): Ditto.
(child_thread_alive): Ditto.
(cygwin_pid_to_str): Ditto.
(handle_load_dll): Reorganize, add first attempt at reading
dll names from attached processes.  Change info messages to provide
more information when dll is already loaded.
(handle_exception): Changes mandated by new thread-aware structures.
(child_wait): Track thread creation/destruction.  Handle cygwin
signals.
(child_create_inferior): Ditto.
(child_resume): Ditto.
(child_kill_inferior): Ditto.  Close child process handle to avoid a
handle leak.
(child_ops): Fill out child_ops fields that deal with threads.
* config/i386/tm-cygwin32.h: Declare function and macro needed
for converting a cygwin "pid" to a string.
* config/i386/xm-cygwin32.h: define HAVE_SIGSETMASK as 0 since
sigsetmask is not defined in cygwin.