Properly fix building with HarfBuzz and without libotf

Properly fix building with HarfBuzz and without libotf

HarfBuzz support does not depend on libotf, the build breakage when
libotf is missing was because code guarded with:

 #if defined HAVE_M17N_FLT && defined HAVE_LIBOTF

was incorrectly changed to:

 #if defined HAVE_M17N_FLT || defined HAVE_HARFBUZZ

this is now properly fixed by making it:

 #if (defined HAVE_M17N_FLT && defined HAVE_LIBOTF) || defined HAVE_HARFBUZZ

Other changes in previous commits were reverted.