NimGL binding generator creates non-ordinal enums with holes.
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* **What is the current behaviour?**

NimGL generates enums with holes, which is "unsafe".

I see 3 solutions here:
1. Disable the warnings for the modules, for now. Should work as far as those enums are used as flags.
2. Fill the enums with unknown/empty values. This is the simplest solution, to not to break compatibility but adds lots of 'fake' symbols, which is undersirable, IMHO.
3. Replace the enums that are used only as flags with constants. This breaks API compatibility if enums are used as {.pure.} enums and used as `EnumType.EnumValue`, instead of `EnumValue`. This may cause collisions, therefore prefixes for enums should be used. For example, for the `ImguiHovereredFlags` example, instead of `ImguiHoveredFlags.AnyWindow` it mus generate somthing like `ighfAnyWindow`.

I'm not sure what's the best solution here :(

* **Please provide the steps to reproduce and if possible a minimal demo of the problem**

See `ImGuiHoveredFlags`, for example.

* **What is the expected behaviour?**

Compile without warnings.

* **Please tell us about your environment**

  - Version: [ 1.3.2 ]
  - OS: [ Linux ]
  - Bindings: [ ImGui, but potentially any other bindings ]
  - Backend: [ C | CPP ]

* **Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, docs.gl, documentation etc)

Building with nim, verbosity set to 1, you get:
```
/home/kraptor/.nimble/pkgs/nimgl-1.3.2/nimgl/imgui.nim(2748, 51) Warning: conversion to enum with holes is unsafe: ImGuiHoveredFlags(0) [HoleEnumConv]
/home/kraptor/.nimble/pkgs/nimgl-1.3.2/nimgl/imgui.nim(2748, 51) Warning: conversion to enum with holes is unsafe: ImGuiHoveredFlags(0) [HoleEnumConv]
/home/kraptor/.nimble/pkgs/nimgl-1.3.2/nimgl/imgui.nim(2816, 68) Warning: conversion to enum with holes is unsafe: ImGuiPopupFlags(0) [HoleEnumConv]
```