write_pieced_value: Notify memory_changed observers

write_pieced_value: Notify memory_changed observers

So far write_pieced_value uses write_memory when writing memory pieces to
the target.  However, this is a case where GDB potentially overwrites a
watchpoint value.  In such a case write_memory_with_notification should be
used instead, so that memory_changed observers get notified.

gdb/ChangeLog:

	* dwarf2loc.c (write_pieced_value): When writing the data for a
	memory piece, use write_memory_with_notification instead of
	write_memory.