pathplan: add support for the dllexport storage-class attribute in vis.h

Also, storage-class attributes are now added only when the GVDLL
symbol is defined.

This will allow removing the viz.h symbols from the pathplan.def file
in an upcoming commit.

Towards https://gitlab.com/graphviz/graphviz/-/issues/2058.

diff --git a/lib/pathplan/vis.h b/lib/pathplan/vis.h
index c8c3e20b613a2740ba1ddcb29146fb5586d68534..da23c37df93666211ec2e21268dd987190e0934b 100644 (file)
--- a/lib/pathplan/vis.h
+++ b/lib/pathplan/vis.h
@@ -38,8 +38,10 @@ extern "C" {
        /* this is computed from the above */
        array2 vis;
     };
-#ifdef _WIN32
-#ifndef PATHPLAN_EXPORTS
+#ifdef GVDLL
+#ifdef PATHPLAN_EXPORTS
+#define VIS_API __declspec(dllexport)
+#else
 #define VIS_API __declspec(dllimport)
 #endif
 #endif