Compiler Failure

This was working before I made changes to workaround extending throwable and the underscore issue in java.

git version of Haxe.

```
haxelib install moon-run
sudo haxelib run moon-run setup
git clone --branch develop https://github.com/ohmrun/stx_pico && cd stx_pico
hx build unit/cpp
```

```
Haxe: 4.3.0-rc.1; OS type: unix;
File "src/generators/gencpp.ml", line 4589, characters 26-33
Called from Gencpp.gen_field in file "src/generators/gencpp.ml", line 4589, characters 19-33
Called from Stdlib__list.iter in file "list.ml", line 110, characters 12-15
Called from Gencpp.generate_class_files.generate_class_cpp in file "src/generators/gencpp.ml", line 6046, characters 3-159
Called from Stdlib__list.iter in file "list.ml", line 110, characters 12-15
Called from Gencpp.generate_source in file "src/generators/gencpp.ml", line 8512, characters 3-39
Called from Haxe.generate in file "src/compiler/haxe.ml", line 346, characters 2-14
Called from Haxe.init in file "src/compiler/haxe.ml", line 1080, characters 25-72
Called from Haxe.process_params.loop in file "src/compiler/haxe.ml", line 645, characters 3-11
Called from Haxe in file "src/compiler/haxe.ml", line 1245, characters 1-35
File "src/core/globals.ml", line 117, characters 1-7: Assertion failed
```

Reproduce the failure with the listed haxelib, git clone, and `hx build unit/cpp` commands. Then inspect `src/generators/gencpp.ml` at line 4589 and `src/core/globals.ml` at line 117, using the stack trace as the starting point. Done means the reported build no longer fails with the assertion.

Written by the indexing model from the issue text.