src/posix.c: HAVE_STAT_TV_NSEC seems not to be declared anywhere

[mgorny]

Looking through the code in src/posix.h, I see:

#ifdef HAVE_STAT_TV_NSEC
    self->mtime_nsec = st.st_mtim.tv_nsec;
#else
    self->mtime_nsec = 0;
#endif

But there's no platform check defining the define!

[radhermit]

Closing since I think the related fixes were merged a while ago.