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

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

diff --git a/lib/cgraph/agxbuf.h b/lib/cgraph/agxbuf.h
index cd2dd424144fbb44a75e42ee15505590d32ad72a..9e9d70800c785862eedc85d498376ce901f214e3 100644 (file)
--- a/lib/cgraph/agxbuf.h
+++ b/lib/cgraph/agxbuf.h
@@ -18,7 +18,7 @@ extern "C" {
 
 #include "config.h"
 
-#ifdef _WIN32
+#ifdef GVDLL
 #ifdef EXPORT_AGXBUF
 #define AGXBUF_API __declspec(dllexport)
 #else