cgraph++: use GVDLL instead of _WIN32 to control storage-class attributes in AGraph.h

Towards https://gitlab.com/graphviz/graphviz/-/issues/2173.

diff --git a/lib/cgraph++/AGraph.h b/lib/cgraph++/AGraph.h
index fc779472e86ea561ab4aeb581bd7bd223a14285f..16d77343ac6b496ac14fb6994c91b2dca488ce9b 100644 (file)
--- a/lib/cgraph++/AGraph.h
+++ b/lib/cgraph++/AGraph.h
@@ -5,7 +5,7 @@
 
 #include <cgraph/cgraph.h>
 
-#ifdef _WIN32
+#ifdef GVDLL
 #if cgraph___EXPORTS // CMake's substitution of cgraph++_EXPORTS
 #define AGRAPH_API __declspec(dllexport)
 #else