Add glfw's splitview.c example

When compiling this example there are lots of this warnings

```
 The origin of the name <GLsizei> in [MODULE examples-glfw-splitview] is ambiguous, could be {<GLsizei> in calvino-glu} or {<GLsizei> in calvino-gl-legacy}.  Will use {<GLsizei> in calvino-glu}.
```

Any way to silence them?