c11: Import threads.h emulation library.

c11: Import threads.h emulation library.

Implementation is based of https://gist.github.com/2223710 with the
following modifications:
- inline implementatation
- retain XP compatability
- add temporary hack for static mutex initializers (as they are not part
  of the stack but still widely used internally)
- make TIME_UTC a conditional macro (some system headers already define
  it, so this prevents conflict)
- respect HAVE_PTHREAD macro

Reviewed-by: Brian Paul <brianp@vmware.com>
Acked-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Chad Versace <chad.versace@linux.intel.com>