Fix new error with Clang 6.x:

exec.cpp:438:8: error: case value evaluates to 2684500526, which cannot be narrowed to type 'int32_t' (aka 'int')
      [-Wc++11-narrowing]
                case 0xA0023A2E:
                     ^

The switch cases were unsigned, but the passed value was an int32.