Bug 696376 - Change how we find critical ranges so that it works on 10.6 too. r=dbaron.

Currently we use dlsym on pthread_cond_wait$UNIX2003 to find a
function that indicates that new_sem_from_pool is on the stack. This
works on 10.5, but on 10.6 I could not find a single reliable
indicator that would work with dlsym.

The good news is that dladdr works with any symbol, not just exported
ones. To find the address of new_sem_from_pool, we set up a malloc logger
and force a call to new_sem_from_pool. From the logger callback we walk
the stack trying dladdr on every address.

To force a call to new_sem_from_pool, the initialization code has to be the
first to use semaphores, so it is now run from NS_LogInit.

This works on 10.6 and 10.5 (but we have to look for
"pthread_cond_wait$UNIX2003"). In 10.7 the call to malloc is gone, so we don't
have to worry about critical addresses on it anymore.

tools/trace-malloc/lib/nsTraceMalloc.c

@@ -957,7 +957,7 @@ backtrace(tm_thread *t, int skip, int *immediate_abort)
     t->suppress_tracing++;
 
     if (!stacks_enabled) {
-#if defined(XP_MACOSX) && defined(__i386)
+#if defined(XP_MACOSX)
         /* Walk the stack, even if stacks_enabled is false. We do this to
            check if we must set immediate_abort. */
         info->entries = 0;