Make it produce a useable dll/lib under Windows

jmorecfg.h

@@ -242,11 +242,16 @@ typedef unsigned int JDIMENSION;
 #define METHODDEF(type)		static type
 /* a function used only in its module: */
 #define LOCAL(type)		static type
+
+#ifdef _WIN32
+#define GLOBAL(type)	__declspec(dllexport) type 
+#define EXTERN(type)	extern __declspec(dllexport) type
+#else
 /* a function referenced thru EXTERNs: */
 #define GLOBAL(type)		type
 /* a reference to a GLOBAL function: */
 #define EXTERN(type)		extern type
-
+#endif
 
 /* This macro is used to declare a "method", that is, a function pointer.
  * We want to supply prototype parameters if the compiler can cope.