(update_watchpoint): Set and clear val_valid. Use
fetch_watchpoint_value. Handle unreadable values on the
value chain. Correct check for user-requested array watchpoints.
(breakpoint_init_inferior): Clear val_valid.
(watchpoint_value_print): New function.
(print_it_typical): Use it. Do not free or clear old_val. Print
watchpoints even if old_val == NULL.
(watchpoint_check): Use fetch_watchpoint_value. Check for values
becoming readable or unreadable.
(watch_command_1): Use fetch_watchpoint_value. Set val_valid.
(do_enable_watchpoint): Likewise.
* breakpoint.h (struct breakpoint): Update comment for val. Add
val_valid.
* NEWS: Mention watchpoints on inaccessible memory.
* gdb.base/watchpoint.c (global_ptr, func4): New.
(main): Call func4.
* gdb.base/watchpoint.exp: Call test_inaccessible_watchpoint.
(test_inaccessible_watchpoint): New.
* gdb.texinfo (Set Watchpoints): Mention watchpoints on
unreadable memory. Delete obsolete SPARClite reference.
