Last week, someone noted that a couple of the time_point member functions were not...

Last week, someone noted that a couple of the time_point member functions were not constexpr. I looked, and they were right. They were made constexpr in p0505, so I looked at all the other bits in that paper to make sure that I didn't miss anything else. There were a couple methods in the synopsis that should have been marked constexpr, but the code was correct.

llvm-svn: 340992