Updated waf to 1.9.9.

NEW IN WAF 1.9.9
----------------
* Fix QT5 detection on macOS 1912
* Fix Clang compilation database when no c compiler is found #1914
* Fix python 3 compatibility with cppcheck #1921
* Fix the thread index in parallel_debug
* Fix install task for mac_files #1911
* Fix msvc version detection #1907
* Add VS2017 support #1927
* Add newer fortran flag detection #1916
* Add unity builds settings per task generator
* Add run_build_cls parameter to conf.run_build/conf.check
* Add a warning for missing cflags/cxxflags in gccdeps

(wiz)