[turbofan] Overload the -- operator under the LookupReturn Iterator

Changes introduced in 30ec6a89 generates compilation error in gcc 8.1.0:

8.1.0/include/c++/bits/stl_iterator_base_funcs.h:183:2:
error: no match for 'operator--' (operand type is
'v8::internal::HandlerTable::LookupReturn(int)::Iterator')
--__i;

Which maybe caused by the following change in stl_iterator_base_funcs:
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=248875

Overloading the "--" operator fixes the compilation error.


Change-Id: I32f54ddd4993375bf905996b5b1e66cd005256da
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1888190
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64624}

src/codegen/handler-table.cc

@@ -203,6 +203,10 @@ int HandlerTable::LookupReturn(int pc_offset) {
       index++;
       return *this;
     }
+    Iterator& operator--() {
+      index--;
+      return *this;
+    }
     Iterator& operator+=(difference_type offset) {
       index += offset;
       return *this;