Better selection of homegrown ino_t in vmsish.h.

Better selection of homegrown ino_t in vmsish.h.

We had been using a 64-bit definition of myino_t only when
_LARGEFILE is defined, but we actually get large file support via
either _LARGEFILE or _USE_STD_STAT because both give us 64-bit
off_t, so look at both definitions.

The size of off_t is not any great indicator for the size of
ino_t, but this preserves the intent of the existing code.

TODO: figure out when _USE_STD_STAT became available; it's
possible we no longer need this hackish layer on top of the
stat struct.