Work around conda-forge's CDT version of GL (#983)

* Work around conda-forge's CDT version of GL

Signed-off-by: Michael Carroll <mjcarroll@intrinsic.ai>
Co-authored-by: Silvo Traversaro <silvio@traversaro.it>

* Remove unnecessary preprocessor

Signed-off-by: Michael Carroll <mjcarroll@intrinsic.ai>

---------

Signed-off-by: Michael Carroll <mjcarroll@intrinsic.ai>
Co-authored-by: Silvo Traversaro <silvio@traversaro.it>

ogre/src/OgreRenderEngine.cc

@@ -19,6 +19,14 @@
 #if !defined(__APPLE__) && !defined(_WIN32)
 # include <X11/Xlib.h>
 # include <X11/Xutil.h>
+
+// conda-forge's glext.h is old and has a bug.
+// This is a minimally-intrusive fix to correct types.
+// On modern GL distributions, glx.h will override these.
+# include <KHR/khrplatform.h>
+typedef khronos_ssize_t GLsizeiptr;
+typedef khronos_intptr_t GLintptr;
+
 # include <GL/glx.h>
 #endif