ftinspect: compile warning on MSVC about int->FTC_FaceID conversion

MSVC complains when compiling ftinspect code:

engine.cpp(265): warning C4312: 'reinterpret_cast': conversion from 'T' to 'void *' of greater size
          with
          [
              T=int
          ]

The affected code is like:

FTC_FaceID ftcFaceID = reinterpret_cast<void*>
                           (faceIDMap.value(FaceID(fontIndex,
                                                   0,
                                                   0)));
.....
ftcFaceID = reinterpret_cast<void*>(faceCounter);

where faceCounter and value return from faceIDMap.value are all int.

There're two possible solutions:

1. Use intptr_t in favor of int. This enables 8 bytes long face id on 64 bit machines. The faceIDMap and faceCounter would be redefined (maybe we need type aliasing);
2. Cast int to intptr_t at all sites of conversion. This can ensure consistent behavior on 32 and 64 bit machines.

Which solution should be preferred?