Another Cygwin fix. This seems to take care of things proeprly.

simgear/screen/extensions.hxx

@@ -24,10 +24,6 @@
 #ifndef __SG_EXTENSIONS_HXX
 #define __SG_EXTENSIONS_HXX 1
 
-#if !defined(WIN32)
-# include <dlfcn.h>
-#endif
-
 #if defined(__CYGWIN__)  /* && !defined(USING_X) */
 #define WIN32
 #endif
@@ -36,6 +32,10 @@
 # include <windows.h>
 #endif
 
+#if !defined(WIN32)
+# include <dlfcn.h>
+#endif
+
 #include <GL/gl.h>
 
 
@@ -57,7 +57,7 @@ bool SGIsOpenGLExtensionSupported(char *extName);
 
 inline void (*SGLookupFunction(const char *func))()
 {
-#if defined( WIN32 ) && !defined(__CYGWIN__) && !defined(__MINGW32__)
+#if defined( WIN32 )
     return (void (*)()) wglGetProcAddress(func);
 
 #elif defined( __APPLE__ )