add gcc version check to gl.h to avoid warnings
|Reported by:||jstressman||Owned by:||kallisti5|
Currently (hrev44524) when building things like SDL, we get thousands of warning messages about "warning: `visibility' attribute directive ignored"
A version check to not use this attribute unless we have a higher GCC version avoids this.
The attached patch fixes the problem for me, but I'd like for someone more knowledgeable to have a look. :)