fiddle test_qsort fails

[ahorek]

Environment
jruby 9.2.10.0-SNAPSHOT (2.5.7) 2019-11-08 c56caa3 Java HotSpot(TM) 64-Bit Server VM 11.0.2+9-LTS on 11.0.2+9-LTS +jit [linux-x86_64]
Linux DESKTOP-2POPPQP 4.4.0-17763-Microsoft #864-Microsoft Thu Nov 07 15:22:00 PST 2019 x86_64 x86_64 x86_64 GNU/Linux

I fixed a bunch of bugs in #5960

but in order to support https://github.com/ankane/lightgbm/tree/fiddle
there's one blocker which I don't know how to fix

a simple test case

jruby/test/mri/fiddle/test_func.rb

Line 73 in 4e8bb26

def test_qsort1

Expected Behavior
test passes

Actual Behavior

Fiddle::TestFunc#test_qsort1:
TypeError: cannot convert parameter to native pointer

this code tries to convert the class into a pointer

jruby/core/src/main/java/org/jruby/ext/ffi/jffi/JITRuntime.java

Line 530 in 42ae3ed

} else if (parameter.respondsTo("to_ptr")) {

[ahorek]

• the same issue as Fiddle implementation on FFI does not properly handle type conversions #7307