[NFC][lsan] Use kIgnored in MarkInvalidPCCb

kIgnored didn't exist when the code was added, but it should be
equivalent to kReachable.
The goal is to refactor MarkInvalidPCCb to avoid StackDepotGet
in StopTheWorld.

compiler-rt/lib/lsan/lsan_common.cpp

@@ -505,7 +505,7 @@ static void MarkInvalidPCCb(uptr chunk, void *arg) {
     // it as reachable, as we can't properly report its allocation stack anyway.
     if (caller_pc == 0 || (param->skip_linker_allocations &&
                            GetLinker()->containsAddress(caller_pc))) {
-      m.set_tag(kReachable);
+      m.set_tag(kIgnored);
       param->frontier->push_back(chunk);
     }
   }