Updated to build against xorg-x11-server 1.16.0.
LoadExtensionList is new in 1.16.
Another LoadExtensionList() that needs an #ifdef.
No need to declare 'display' here.
GCFuncs and GCOps are const since 1.16.
No need to declare 'display' here either.
Fix linking when dri3 and present are enabled.
Merge branch 'xorgserver116' of https://github.com/twaugh/tigervnc