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

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

diff --git a/lib/cgraph/cgraph.h b/lib/cgraph/cgraph.h
index 7de0cc137bdd2ccd0d5a2920ce1e385cc8f174ec..87936f74a36d495091176856356d78d1f39f1d35 100644 (file)
--- a/lib/cgraph/cgraph.h
+++ b/lib/cgraph/cgraph.h
@@ -17,7 +17,7 @@
 extern "C" {
 #endif
 
-#ifdef _WIN32
+#ifdef GVDLL
 #ifdef EXPORT_CGRAPH
 #define CGRAPH_API __declspec(dllexport)
 #else