glx: Fix up glXQueryGLXPbufferSGIX on macOS.
Fix this build error on macOS.
../src/glx/apple/glx_empty.c:158:4: error: void function 'glXQueryGLXPbufferSGIX' should not return a value [-Wreturn-type] return 0; ^ ~
Fixes: 3dd299c3 ("glx: Sync <GL/glxext.h> with Khronos") Signed-off-by: Vinson Lee vlee@freedesktop.org