fbc: github # 318: duplicate definition for deleting destructor

- the deleting destructor was being automatically generated (implementation) even when the class (UDT) was being declared only
- remove automatic implementation (definition) of the deleting destructor (g++ compatibility)
- add tests for (simplified) virtual destructor and method in tests/cpp/derived.bmk
- add method test for class test in tests/cpp/class.bmk

changelog.txt

@@ -7,6 +7,7 @@ Version 1.08.1
 
 [fixed]
 - github #315: set parameters when calling SCREENCONTROL (was broken in fbc 1.08.0 due to new LONG/LONGINT SCREENCONTROL API's)
+- github #318: duplicate definition for deleting destructor; the deleting destructor was being emitted even though the class was declarations only on the fbc side
 
 
 Version 1.08.0