makepanda: Update checkPandaVersion.h

This makes it possible to include it multiple times in a single
translation unit, and/or multiple times in a single dynamic
library (and without excess code bloat, too).

makepanda/makepanda.py

@@ -2606,18 +2606,21 @@ PANDAVERSION_H_RUNTIME="""
 
 CHECKPANDAVERSION_CXX="""
 # include "dtoolbase.h"
-EXPCL_DTOOL_DTOOLUTIL int panda_version_$VERSION1_$VERSION2 = 0;
+EXPCL_DTOOL_DTOOLBASE int panda_version_$VERSION1_$VERSION2 = 0;
 """
 
 CHECKPANDAVERSION_H="""
+# ifndef CHECKPANDAVERSION_H
+# define CHECKPANDAVERSION_H
 # include "dtoolbase.h"
-extern EXPCL_DTOOL_DTOOLUTIL int panda_version_$VERSION1_$VERSION2;
-# ifndef WIN32
-/* For Windows, exporting the symbol from the DLL is sufficient; the
-      DLL will not load unless all expected public symbols are defined.
-      Other systems may not mind if the symbol is absent unless we
-      explictly write code that references it. */
-static int check_panda_version = panda_version_$VERSION1_$VERSION2;
+extern EXPCL_DTOOL_DTOOLBASE int panda_version_$VERSION1_$VERSION2;
+// Hack to forcibly depend on the check
+template<typename T>
+class CheckPandaVersion {
+public:
+  int check() { return panda_version_$VERSION1_$VERSION2; }
+};
+template class CheckPandaVersion<void>;
 # endif
 """