remove open coded strcasecmp
Graphviz contains three implementations of the function
strcasecmp and two implementations of the function
strncasecmp. It looks like these were added as there was no cross-platform alternative at the time.
At the time of writing, every major platform I'm aware of implements
strncasecmp except Windows. Windows also has this functionality, but under the names
I propose we remove these implementations and replace them with a small compatibility header that provides
strncasecmp on Windows by redirecting to the alternatives. I'm creating this issue to see what others' opinions are. Maybe it would be better to hold off until we move to C99 in December 2020? I don't believe this will make a difference because these two functions are not standardized in C99 but rather in POSIX 2001, but maybe someone has a different opinion.