sim: Fix erasure ordering in the futex map.

Erase an element after one of its components are used to erase an
element of another map. This is an error and causes build breakage in
newer versions of gcc.

Change-Id: I83a00410cbf2ae5fc23b12080cd374965df1a5ac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60309
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/sim/futex_map.cc

@@ -123,8 +123,8 @@ FutexMap::wakeup_bitset(Addr addr, uint64_t tgid, int bitmask)
 
         if (waiter.checkMask(bitmask)) {
             waiter.tc->activate();
-            iter = waiterList.erase(iter);
             waitingTcs.erase(waiter.tc);
+            iter = waiterList.erase(iter);
             woken_up++;
         } else {
             ++iter;