New review comment by classabbyamp on void-packages repository

https://github.com/void-linux/void-packages/pull/39984#discussion_r997598708

Comment:
```suggestion
CFLAGS="-DSEMINIT -I. -I${XBPS_CROSS_BASE}/usr/include/GL -I${XBPS_CROSS_BASE}/usr/X11/include -I../../libSNL/src -I../../glut-3.5/src"
```
only need to include the special cflags