Log Message:
Update waf to 1.8.16:

NEW IN WAF 1.8.16
-----------------
* Reverted the changes to conf.check(header_name=) as this causes
  regressions. Use conf.check(header_name=, link_header_test=False)
  - #1647
* Disabled the loading of c_emscripten when building from the Waf tree
* Fixed the documentation build when using Sphinx < 1.3
* Propagate ldflags/LDFLAGS besides linkflags/LINKFLAGS
* Python3 fixes in extras/file_to_object.py

Fixes build of multimedia/mpv.