set if ignore_non_function is set.
* gprof.h (ignore_non_functions): Declare.
* gprof.c (ignore_non_functions): Define.
(long_options): Add "ignore-non-functions".
(usage): Add new options.
(main): Recognize "-D" and "--ignore-non-functions" option.
So we can get more accurate information on Solaris, HPUX and other
systems that can uniquely identify function symbols.