glx: reorder things a bit to make it build on Apple platforms again
What does this MR do and why?
env
was defined in an #ifdef'ed section, and then checked at https://gitlab.freedesktop.org/K900/mesa/-/blob/6985dd0d9b877cbf1ca6119339cb24812833e4e8/src/glx/glxext.c#L947, which is not #ifdef'ed, so the build failed. Hoist it out of the ifdef to get things building again. This does technically introduce an unnecessary environment access, but it's probably not a big deal?