[graphviz-interest] About ifdefs for custom defines in public headers (e.g. HAVE_STRING_H in cdt.h)

Hey,

I've noticed that since GraphViz 2.36.0 (I think) 'cdt.h' checks for 
HAVE_STRING_H and other defines. cdt.h is a public header that may be used in 
other applications.

Relevant code:
#ifdef HAVE_STRING_H
#include <string.h>
#else
extern int		memcmp _ARG_((const Void_t*, const Void_t*, size_t));
extern int		strcmp _ARG_((const char*, const char*));
#endif

So, if HAVE_STRING_H is not defined, this leads to problems like discussed in 
https://github.com/KDAB/GammaRay/issues/70.
(Note: GammaRay uses libgraphviz and includes cdt.h)

IMO, from a technical POV you shouldn't check against macros that you don't 
define yourself in publicly installed headers, which is the case for 
HAVE_STRING_H. Public headers should be self-contained and should not require 
an external user to define custom defines in order to make it work.

Almost every external user of the library will now have to provide 
HAVE_STRING_H=1 in his build system to be able to compile this file.

Are you aware of the issue? Do you need more details?

Cheers

-- 
Kevin Funk
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