c11: reinstate the original license and authorship
The original code that was copied in was Boost licensed, so keep that in. Since Yonggang Luo has code quite some work, keep their copyright alongside the original one.
Fixes: b2ddec4e ("c11: Implement c11/time.h with c11/impl/time.c") Fixes: e6392fcf ("c11: Move the implementation of threads.h into c source code")
@lygstate an Ack/RB would be appreciated?