Fixing warnings under GCC4 in preparation to enable -Werror there as well:

* Replaced the use of offsetof() for structs that aren't PODs. Add a
  offset_of_member() macro to util/khash.h because that's what it's used for
  in our cases.
* Change the signature of add_debugger_command()/remove_debugger_command() on
  GCC > 2 to avoid the depricated conversion from string constants to char *.
* Adding some "suggested" parenthesis. I know that not everyone likes that, but
  it pointed out at least one bug that is fixed here as well.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29113 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/wait_for_objects.cpp

@@ -564,7 +564,7 @@ common_poll(struct pollfd *fds, nfds_t numFDs, bigtime_t timeout, bool kernel)
 		int fd = fds[i].fd;
 
 		// initialize events masks
-		sync->set[i].selected_events = fds[i].events & ~POLLNVAL
+		sync->set[i].selected_events = (fds[i].events & ~POLLNVAL)
 			| POLLERR | POLLHUP;
 		sync->set[i].events = 0;