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

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

diff --git a/lib/xdot/xdot.h b/lib/xdot/xdot.h
index e66adf97adeda7e6bf98b6495732cb689f69cee4..cc67f9a224f7a4bbdf2df296d2667467e92588b5 100644 (file)
--- a/lib/xdot/xdot.h
+++ b/lib/xdot/xdot.h
@@ -16,7 +16,7 @@
 extern "C" {
 #endif
 
-#ifdef _WIN32
+#ifdef GVDLL
 #ifdef EXPORT_XDOT
 #define XDOT_API __declspec(dllexport)
 #else