DefaultIOSystem: close cygwin issue assimp/assimp/issues/660.

code/DefaultIOSystem.cpp

@@ -135,11 +135,11 @@ inline void MakeAbsolutePath (const char* in, char* _out)
 {
     ai_assert(in && _out);
     char* ret;
-#if defined _WIN32 && defined _MSC_VER
-	ret = ::_fullpath( _out, in, PATHLIMIT );
+if defined( _MSC_VER ) || defined( __MINGW32__ )
+    ret = ::_fullpath( _out, in, PATHLIMIT );
 #else
-        // use realpath
-        ret = realpath(in, _out);
+    // use realpath
+    ret = realpath(in, _out);
 #endif
     if(!ret) {
         // preserve the input path, maybe someone else is able to fix