graphviz: patch broken cdt.h header file

The cdt.h header duplicates the signatures of standard library functions
memcmp() and strcpy(), but those signatures don't match the real thing when
building with a C++ compiler, because they lack the no-throw declaration glibc
has. Simply dropping those redundant prototypes remedies the issue.

pkgs/tools/graphics/graphviz/default.nix

@@ -15,6 +15,8 @@ stdenv.mkDerivation rec {
       pango gd gts
     ] ++ stdenv.lib.optionals (xlibs != null) [ xlibs.xlibs xlibs.libXrender ];
 
+  patches = [ ./fix-broken-memcp-signature.patch ];
+
   configureFlags =
     [ "--with-pngincludedir=${libpng}/include"
       "--with-pnglibdir=${libpng}/lib"

pkgs/tools/graphics/graphviz/fix-broken-memcp-signature.patch

@@ -0,0 +1,15 @@
+diff -ubr graphviz-2.28.0-orig/lib/cdt/cdt.h graphviz-2.28.0-new/lib/cdt/cdt.h
+--- graphviz-2.28.0-orig/lib/cdt/cdt.h	2012-11-11 20:05:55.674397100 +0100
++++ graphviz-2.28.0-new/lib/cdt/cdt.h	2012-11-11 20:06:28.069511092 +0100
+@@ -238,11 +238,6 @@
+ extern int		dtstat _ARG_((Dt_t*, Dtstat_t*, int));
+ extern unsigned int	dtstrhash _ARG_((unsigned int, Void_t*, int));
+ 
+-#if !_PACKAGE_ast
+-extern int		memcmp _ARG_((const Void_t*, const Void_t*, size_t));
+-extern int		strcmp _ARG_((const char*, const char*));
+-#endif
+-
+ #undef extern
+ _END_EXTERNS_
+