PowerPC 64-bit time_t

[Justin Hibbits]

At the devsummit earlier today I mentioned for FreeBSD 12 wanting 64- 
bit time_t across the board.  It was pointed out that the only ones  
with 32-bit time_t are i386 and powerpc (32-bit).  I've made the  
changes necessary for at least kernel (world is still building right  
now), but it's obviously an ABI and KBI incompatible change.   
Addressing KBI is a nonissue, as that's expected to break at major  
releases.  ABI is another issue.  I'm unsure how to properly address  
ABI breakage -- bumping libc's .so version, or reversion all symbols  
that use something with time_t, or something else.  If I can address  
it before the code freeze, it could be done for FreeBSD 11, which  
leaves about 6 hours from now.

Any thoughts?

- Justin