'make html' warnings in master branch

[Greg Ercolano]

Just cloned the repo, getting these warnings from 'make html' on the master branch:

Converting Doxyfile to doxygen version 1.8.17
Generating HTML documentation
/usr/local/src/fltk-1.5.x.git/src/Fl_lock.cxx:91: warning: documented symbol 'int Fl_System_Driver::push_awake_handler' was not declared or defined.
/usr/local/src/fltk-1.5.x.git/src/Fl_lock.cxx:151: warning: documented symbol 'int Fl_System_Driver::pop_awake_handler' was not declared or defined.
/usr/local/src/fltk-1.5.x.git/src/Fl_lock.cxx:173: warning: documented symbol 'bool Fl_System_Driver::awake_ring_empty' was not declared or defined.
Built target html