Use consistent conditionals in render_system.hpp (#1294)

These header files define the XVisualInfo type, which is used later in
this header based on different conditionals. In particular, the
evaluation of these conditionals differ on BSD, which appears to have
the headers needed so I don't believe that __linux__ is the correct
conditional to use.

Signed-off-by: Scott K Logan <[email protected]>

Author: cottsay

rviz_rendering/include/rviz_rendering/render_system.hpp

@@ -42,7 +42,7 @@
 
 #include <QDir>  // NOLINT cpplint cannot handle include order here
 
-#ifdef __linux__
+#if !defined(__APPLE__) && !defined(_WIN32)
 
 #include <X11/Xutil.h>
 #include <GL/glx.h>