BUG: bad clipping on macOS arm64

[dsvensson]

The following clipping bug seems to happen on a number of Quake engines, QuakeSpasm, ezQuake, FTE (but not via WebGL):

sezero/quakespasm#80

The effect is that if a triangle is about 50% outside of view it has a risk of being clipped. This is mostly happening with an non-transformed view, directly at spawn at dm3 RL moving straight forward with arrow keys is a great place to reproduce. I haven't verified in ezQuake via debugger, but it's mentioned that when two vertices share the same position, with a negative w component this may happen on iPad, which is close enough to apply to MacBooks as well.

Potential clue:
https://gamedev.net/forums/topic/609483-ipadopengl-es-20-a-triangle-disappears-at-particlular-camera-view/
http://web.archive.org/web/20150908203347/http://fly.srk.fer.hr/~unreal/theredbook/appendixg.html

OpenGL might not handle homogeneous clip coordinates with w < 0 correctly. To be sure that your code is portable to all OpenGL systems, use only nonnegative w values.

[dsvensson]

If tesselation produces a triangle of ~zero area (collinear triangle), this happens. Fix tesselation to avoid this.