The code used to check this symbol, but commit 689abf4 replaced it with
GLX_H, presumably to work better with either Mesa or Khronos headers.
But nVidia's header use the older include guard. Add it as another
option.
Should fix the headerguards.c compile test when the system glx.h is from
nVidia's binary drivers.
We can't completely avoid it, since gl's headers use these defines for
their header guards, and we really do need to stop the system GL
headers from doing anything.
Fixes#14
I was thinking at one point that part of the build was going to
require not including the #defines from the generated code, but would
want these prototypes. It turns out that's not the case (and if it
is, I'll just wrap the #defines in an ifdef).
Bryan Kadzban
Yaron Cohen-Tal
Eric Anholt