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

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

diff --git a/lib/gvc++/GVRenderData.h b/lib/gvc++/GVRenderData.h
index 94cdd4d9d254735fe2e9f96c4fb951b89bc8708e..8ea7312a02d419815368bdf7dbfe18d5eb031554 100644 (file)
--- a/lib/gvc++/GVRenderData.h
+++ b/lib/gvc++/GVRenderData.h
@@ -3,7 +3,7 @@
 #include <cstddef>
 #include <string_view>
 
-#ifdef _WIN32
+#ifdef GVDLL
 #if gvc___EXPORTS // CMake's substitution of gvc++_EXPORTS
 #define GVRENDER_API __declspec(dllexport)
 #else